diff --git a/.gitignore b/.gitignore
index 3831f63..53739d4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 *.MD
 !README.md
 !CONTRIBUTING.md
+!SECURITY.md
 benchmark.csv
 
 # Byte-compiled / optimized / DLL files
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 5d813ab..1b45ce2 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,45 +1,49 @@
 # See https://pre-commit.com for more information
 # See https://pre-commit.com/hooks.html for more hooks
 repos:
--   repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: 'v4.5.0'
-    hooks:
-    -   id: trailing-whitespace
-    -   id: end-of-file-fixer
-    -   id: check-yaml
-    -   id: check-added-large-files
-    -   id: destroyed-symlinks
-    -   id: detect-private-key
-    -   id: check-ast
-    -   id: check-case-conflict
-    -   id: debug-statements
-    -   id: fix-encoding-pragma
-    -   id: forbid-submodules
-    -   id: check-symlinks
-    -   id: check-shebang-scripts-are-executable
-    -   id: check-case-conflict
-    -   id: check-added-large-files
-        args: ['--maxkb=4096']
-    -   id: destroyed-symlinks
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: 'v4.5.0'
+  hooks:
+    - id: trailing-whitespace
+    - id: end-of-file-fixer
+    - id: check-yaml
+    - id: check-added-large-files
+    - id: destroyed-symlinks
+    - id: detect-private-key
+    - id: check-ast
+    - id: check-case-conflict
+    - id: debug-statements
+    # Add <# -*- coding: utf-8 -*-> to the top of python files.
+    - id: fix-encoding-pragma
+        # https://github.com/asottile/pyupgrade/issues/748
+        # https://github.com/asottile/pyupgrade/issues/89
+      args: ['--remove']
+    - id: forbid-submodules
+    - id: check-symlinks
+    - id: check-shebang-scripts-are-executable
+    - id: check-case-conflict
+    - id: check-added-large-files
+      args: ['--maxkb=4096']
+    - id: destroyed-symlinks
 
 # YAPF and flake8 need to remain pinned.
--   repo: https://github.com/pre-commit/mirrors-yapf
-    rev: 'v0.32.0' # frozen: v0.32.0
-    hooks:
-    -   id: yapf
-        additional_dependencies: [toml]
+- repo: https://github.com/pre-commit/mirrors-yapf
+  rev: 'v0.32.0' # frozen: v0.32.0
+  hooks:
+    - id: yapf
+      additional_dependencies: [toml]
 
--   repo: https://github.com/pycqa/flake8
-    rev: '6.0.0' # frozen: 6.0.0
-    hooks:
-    -   id: flake8
-        additional_dependencies: [flake8-docstrings]
+- repo: https://github.com/pycqa/flake8
+  rev: '6.0.0' # frozen: 6.0.0
+  hooks:
+    - id: flake8
+      additional_dependencies: [flake8-docstrings]
 
--   repo: https://github.com/PyCQA/bandit
-    rev: '1.7.5'  # Use the sha / tag you want to point at
-    hooks:
-    -   id: bandit
-        args: ['--skip', 'B404,B506,B410,B603,B324', '--level', 'LOW']
+- repo: https://github.com/PyCQA/bandit
+  rev: '1.7.5'  # Use the sha / tag you want to point at
+  hooks:
+    - id: bandit
+      args: ['--skip', 'B404,B506,B410,B603,B324', '--level', 'LOW']
 
 #   -   repo: https://github.com/pre-commit/mirrors-mypy
 #       rev: 'v0.991'
@@ -47,10 +51,15 @@ repos:
 #       -      id: mypy
 #              args: ['--no-strict-optional', '--ignore-missing-imports', '--show-error-context', '--show-error-codes', '--follow-imports', 'silent']
 
--   repo: https://github.com/pycqa/isort
-    rev: '5.12.0'
-    hooks:
-    -   id: isort
+- repo: https://github.com/pycqa/isort
+  rev: '5.12.0'
+  hooks:
+    - id: isort
+
+- repo: https://github.com/asottile/pyupgrade
+  rev: 'v3.15.0'
+  hooks:
+    - id: pyupgrade
 
 #    -   repo: https://codeberg.org/frnmst/licheck
 #        rev: '1.0.0'
@@ -58,35 +67,41 @@ repos:
 #        -   id: licheck
 #            args: ['--configuration-file', '.allowed_licenses.yml']
 
--   repo: https://codeberg.org/frnmst/md-toc
-    rev: '8.2.0'  # or a specific git tag from md-toc
-    hooks:
-    -    id: md-toc
-         args: [-p, 'cmark', '-l6']  # CLI options
+- repo: https://codeberg.org/frnmst/md-toc
+  rev: '8.2.0'  # or a specific git tag from md-toc
+  hooks:
+    - id: md-toc
+      args: [-p, 'cmark', '-l6']  # CLI options
+
+- repo: https://github.com/mgedmin/check-manifest
+  rev: '0.49'
+  hooks:
+    - id: check-manifest
 
--   repo: https://github.com/mgedmin/check-manifest
-    rev: '0.49'
-    hooks:
-    -   id: check-manifest
+      #- repo: https://github.com/rstcheck/rstcheck
+      #  rev: 'v6.2.0'
+      #  hooks:
+      #    - id: rstcheck
+      #      additional_dependencies: ["tomli"]
 
--   repo: local
-    hooks:
-    -   id: unit-tests
-        name: unit tests
-        language: system
-        entry: make test
-        verbose: true
-        always_run: true
-        pass_filenames: false
-    -   id: build-docs
-        name: build docs
-        language: system
-        entry: make doc
-        verbose: true
-        always_run: true
-        pass_filenames: false
+- repo: local
+  hooks:
+    - id: unit-tests
+      name: unit tests
+      language: system
+      entry: make test
+      verbose: true
+      always_run: true
+      pass_filenames: false
+    - id: build-docs
+      name: build docs
+      language: system
+      entry: make doc
+      verbose: true
+      always_run: true
+      pass_filenames: false
 
--   repo: https://github.com/jorisroovers/gitlint
-    rev: 'v0.18.0'
-    hooks:
-    -   id: gitlint
+- repo: https://github.com/jorisroovers/gitlint
+  rev: 'v0.18.0'
+  hooks:
+    - id: gitlint
diff --git a/MANIFEST.in b/MANIFEST.in
index f3fb141..ede3bfb 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,6 +1,7 @@
 global-include LICENSE.txt
 global-include README.md
 global-include CONTRIBUTING.md
+global-include SECURITY.md
 recursive-include md_toc/cmark *.py
 global-exclude *.csv *.txt
 prune assets
diff --git a/Makefile b/Makefile
index bb485c0..a0d8ab1 100644
--- a/Makefile
+++ b/Makefile
@@ -113,13 +113,17 @@ dist:
 
 upload:
 	$(VENV_CMD) \
-		&& twine upload dist/* \
+		&& twine upload --repository md-toc dist/* \
 		&& deactivate
 
 clean:
 	rm -rf build dist *.egg-info tests/benchmark-results
 	# Remove all markdown files except the readmes.
-	find -regex ".*\.[mM][dD]" ! -name 'README.md' ! -name 'CONTRIBUTING.md' -type f -exec rm -f {} +
+	find -regex ".*\.[mM][dD]" \
+		! -name 'README.md' \
+		! -name 'CONTRIBUTING.md' \
+		| -name 'SECURITY.md' \
+		-type f -exec rm -f {} +
 	$(VENV_CMD) \
 		&& $(MAKE) -C docs clean \
 		&& deactivate
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 0000000..7f7dfc8
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,15 @@
+# Security Policy
+
+## Supported Versions
+
+The latest
+[GIT tagged version of md-toc](https://github.com/frnmst/md-toc/tags) is the
+only one supported. When a new version is released, that one will be the only
+one supported.
+
+## Reporting a Vulnerability
+
+Use this
+[Nextcloud form](https://cloud.franco.net.eu.org/apps/forms/s/ozgp2GqH46QMmsE9JPn5aP8B)
+(preferred) or send me an
+[email](https://blog.franco.net.eu.org/about/#contacts)
diff --git a/docs/conf.py b/docs/conf.py
index db9e49b..1ac5ca6 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # md-toc documentation build configuration file, created by
 # sphinx-quickstart on Wed Dec 27 17:32:50 2017.
diff --git a/docs/pre_commit_hook.rst b/docs/pre_commit_hook.rst
index db5b186..3a917dc 100644
--- a/docs/pre_commit_hook.rst
+++ b/docs/pre_commit_hook.rst
@@ -1,14 +1,17 @@
 Pre-commit hook
 ---------------
 
-This repo provides the following :download:`plugin <../.pre-commit-hooks.yaml>` to be used with the `Pre-commit framework <https://pre-commit.com/>`_:
+This repo provides the following :download:`plugin <../.pre-commit-hooks.yaml>` to be used with the `Pre-commit framework <https://pre-commit.com/>`_
 
 .. literalinclude:: ../.pre-commit-hooks.yaml
    :language: yaml
    :caption: The .pre-commit-hooks.yaml file
    :name: .pre-commit-hooks.yaml
 
-Add a ``.pre-commit-config.yaml`` file in the root of your git repo.
+Add a ``.pre-commit-config.yaml`` file in the root of your GIT repo.
+Have a look at the ``/.pre-commit-hooks.yaml`` file of this repository for a
+full example.
+
 These are the default plugin settings
 
 .. code-block:: yaml
@@ -17,8 +20,8 @@ These are the default plugin settings
 
     repos:
     -   repo: https://codeberg.org/frnmst/md-toc
-        # Remember to keep md-toc up-to-date!
-        rev: master  # set a specific git tag
+        # Release updates (ATOM) https://codeberg.org/frnmst/md-toc/tags.atom
+        rev: master # set a GIT tag
         hooks:
         -   id: md-toc
 
@@ -30,49 +33,10 @@ You can override the defaults via the ``args`` parameter, such as
 
     repos:
     -   repo: https://codeberg.org/frnmst/md-toc
-        # Remember to keep md-toc up-to-date!
-        rev: master  # set a specific git tag
+        # Release updates (ATOM) https://codeberg.org/frnmst/md-toc/tags.atom
+        rev: master # set a GIT tag
         hooks:
         -   id: md-toc
             args: [-p, --skip-lines, '1', redcarpet]  # CLI options
 
-This is what I use in some repositories
-
-.. code-block:: yaml
-
-   # See https://pre-commit.com for more information
-   # See https://pre-commit.com/hooks.html for more hooks
-   repos:
-   -   repo: https://github.com/pre-commit/pre-commit-hooks
-       rev: 'v4.4.0'
-       hooks:
-       -   id: trailing-whitespace
-       -   id: end-of-file-fixer
-       -   id: check-yaml
-       -   id: destroyed-symlinks
-       -   id: detect-private-key
-       -   id: check-ast
-       -   id: check-case-conflict
-       -   id: debug-statements
-       -   id: fix-encoding-pragma
-       -   id: forbid-submodules
-       -   id: check-symlinks
-       -   id: check-shebang-scripts-are-executable
-       -   id: check-case-conflict
-       -   id: check-added-large-files
-           args: ['--maxkb=16384']
-       -   id: destroyed-symlinks
-
-   -  repo: https://codeberg.org/frnmst/md-toc
-      # Remember to keep md-toc up-to-date!
-      rev: '8.2.0'  # set a specific git tag
-      hooks:
-      -    id: md-toc
-           args: [-p, 'cmark', '-l6']  # CLI options
-
-   -   repo: https://github.com/jorisroovers/gitlint
-       rev: 'v0.18.0'
-       hooks:
-       -   id: gitlint
-
 Finally, run ``pre-commit install`` to enable the hook.
diff --git a/md_toc/__init__.py b/md_toc/__init__.py
index e0ecc0e..1801ff5 100644
--- a/md_toc/__init__.py
+++ b/md_toc/__init__.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # __init__.py
 #
diff --git a/md_toc/__main__.py b/md_toc/__main__.py
index 5d1e465..f92eff1 100755
--- a/md_toc/__main__.py
+++ b/md_toc/__main__.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # __main__.py
 #
diff --git a/md_toc/api.py b/md_toc/api.py
index 5c1533c..91c10e5 100644
--- a/md_toc/api.py
+++ b/md_toc/api.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # api.py
 #
@@ -249,7 +248,7 @@ def build_toc(
         # and these are translated into '\n' before being returned to the caller.
         # See
         # https://docs.python.org/3/library/functions.html#open-newline-parameter
-        f = open(filename, 'r', newline=None)
+        f = open(filename, newline=None)
 
     # Help the developers: override the list_marker in case
     # this function is called with the default unordered list marker,
@@ -272,7 +271,7 @@ def build_toc(
         loop: bool = True
         line_counter = 1
         while loop:
-            if line_counter > skip_lines or f.readline() == str():
+            if line_counter > skip_lines or f.readline() == '':
                 loop = False
             line_counter += 1
 
@@ -296,7 +295,7 @@ def build_toc(
         if filename != '-':
             # stdin is not seekable.
             file_pointer_pos = f.tell()
-            if f.readline() == str():
+            if f.readline() == '':
                 is_document_end = True
             f.seek(file_pointer_pos)
 
@@ -789,7 +788,7 @@ def remove_html_tags(line: str, parser: str = 'github') -> str:
         ]
 
         for r in regexes:
-            line = re.sub(r, str(), line, flags=re.DOTALL)
+            line = re.sub(r, '', line, flags=re.DOTALL)
 
     return line
 
@@ -975,7 +974,7 @@ def build_anchor_link(
             # This is equivalent to %x in C. In Python we don't have
             # the length problem so %x is equal to %lx in this case.
             # Apparently there is no %l in Python...
-            header_text_trimmed_middle_stage_str = 'part-' + '{0:x}'.format(
+            header_text_trimmed_middle_stage_str = 'part-' + '{:x}'.format(
                 hash)
 
         return header_text_trimmed_middle_stage_str
@@ -1198,7 +1197,7 @@ def get_atx_heading(
                                 or consecutive_escape_characters == 0):
                             tmp = '\u005c'
                         else:
-                            tmp = str()
+                            tmp = ''
                         final_line = ''.join(
                             [final_line[0:i], tmp, final_line[i:]])
                         i += 1 + len(tmp)
@@ -1353,8 +1352,7 @@ def is_valid_code_fence_indent(line: str, parser: str = 'github') -> bool:
     return False
 
 
-def is_opening_code_fence(line: str,
-                          parser: str = 'github') -> typing.Optional[str]:
+def is_opening_code_fence(line: str, parser: str = 'github') -> str | None:
     r"""Determine if the given line is possibly the opening of a fenced code block.
 
     :parameter line: a single markdown line to evaluate.
@@ -1387,7 +1385,7 @@ def is_opening_code_fence(line: str,
         # The info string is the whole line except the first opening code
         # fence markers.
         if line == len(line) * line[0]:
-            info_string = str()
+            info_string = ''
             info_string_start = len(line)
         else:
             # Get the index where the info string starts.
diff --git a/md_toc/cli.py b/md_toc/cli.py
index 58f1855..3b24165 100644
--- a/md_toc/cli.py
+++ b/md_toc/cli.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # cli.py
 #
diff --git a/md_toc/cmark/__init__.py b/md_toc/cmark/__init__.py
index 34186df..64433cb 100644
--- a/md_toc/cmark/__init__.py
+++ b/md_toc/cmark/__init__.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # __init__.py
 #
diff --git a/md_toc/cmark/buffer_c.py b/md_toc/cmark/buffer_c.py
index f0c88e5..47c9de2 100644
--- a/md_toc/cmark/buffer_c.py
+++ b/md_toc/cmark/buffer_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # buffer_c.py
 #
@@ -33,7 +32,7 @@
 # in that case the license header at the top of the file applies.
 # See docs/copyright_license.rst
 
-cmark_strbuf__initbuf: str = str()
+cmark_strbuf__initbuf: str = ''
 
 
 # 0.30
@@ -59,7 +58,7 @@ def _cmark_cmark_strbuf_init(mem: _cmarkCmarkMem, buf: _cmarkCmarkStrbuf,
     buf.mem = mem
     buf.asize = 0
     buf.size = 0
-    buf.ptr = str()
+    buf.ptr = ''
 
     if initial_size > 0:
         _cmark_cmark_strbuf_grow(buf, initial_size)
@@ -114,7 +113,7 @@ def _cmark_cmark_strbuf_clear(buf: _cmarkCmarkStrbuf):
 
     if buf.asize > 0:
         del buf.ptr
-        buf.ptr = str()
+        buf.ptr = ''
 
 
 # 0.29, 0.30
@@ -195,7 +194,7 @@ def _cmark_cmark_strbuf_detach(buf: _cmarkCmarkStrbuf) -> str:
     if buf.asize == 0:
         # return an empty string
         #     return (unsigned char *)buf->mem->calloc(1, 1);
-        return str()
+        return ''
 
     _cmark_cmark_strbuf_init(buf.mem, buf, 0)
     return data
diff --git a/md_toc/cmark/buffer_h.py b/md_toc/cmark/buffer_h.py
index b86b2bb..4d8bd42 100644
--- a/md_toc/cmark/buffer_h.py
+++ b/md_toc/cmark/buffer_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # buffer_h.py
 #
@@ -39,7 +38,7 @@ class _cmarkCmarkStrbuf:
 
     def __init__(self):
         self.mem: _cmarkCmarkMem = None
-        self.ptr: str = str()
+        self.ptr: str = ''
         self.asize: int = 0
         self.size: int = 0
 
diff --git a/md_toc/cmark/chunk_h.py b/md_toc/cmark/chunk_h.py
index 4c3598d..241ee43 100644
--- a/md_toc/cmark/chunk_h.py
+++ b/md_toc/cmark/chunk_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # chunk_h.py
 #
diff --git a/md_toc/cmark/cmark_ctype_c.py b/md_toc/cmark/cmark_ctype_c.py
index 354df2f..98b83bf 100644
--- a/md_toc/cmark/cmark_ctype_c.py
+++ b/md_toc/cmark/cmark_ctype_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # cmark_ctype_c.py
 #
diff --git a/md_toc/cmark/cmark_h.py b/md_toc/cmark/cmark_h.py
index d81c4f2..81c5930 100644
--- a/md_toc/cmark/cmark_h.py
+++ b/md_toc/cmark/cmark_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # cmark_h.py
 #
diff --git a/md_toc/cmark/houdini_h.py b/md_toc/cmark/houdini_h.py
index ca432c6..fa3b2ab 100644
--- a/md_toc/cmark/houdini_h.py
+++ b/md_toc/cmark/houdini_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # houdini_h.py
 #
diff --git a/md_toc/cmark/houdini_html_u_c.py b/md_toc/cmark/houdini_html_u_c.py
index 1ecae84..4bf4a69 100644
--- a/md_toc/cmark/houdini_html_u_c.py
+++ b/md_toc/cmark/houdini_html_u_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # houdini_html_u_c.py
 #
diff --git a/md_toc/cmark/inlines_c.py b/md_toc/cmark/inlines_c.py
index 5f5d6ca..e8cff3f 100644
--- a/md_toc/cmark/inlines_c.py
+++ b/md_toc/cmark/inlines_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # inlines_c.py
 #
@@ -144,7 +143,7 @@ def __init__(self):
         self.next: _cmarkDelimiter = None
         self.inl_text: _cmarkCmarkNode = None
         self.length: int = 0
-        self.delim_char = str()
+        self.delim_char = ''
         self.can_open: bool = False
         self.can_close: bool = False
 
diff --git a/md_toc/cmark/node_c.py b/md_toc/cmark/node_c.py
index 47b5d6c..64415cf 100644
--- a/md_toc/cmark/node_c.py
+++ b/md_toc/cmark/node_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # node_c.py
 #
@@ -104,8 +103,8 @@ def _cmark_S_free_nodes(e: _cmarkCmarkNode):
         if e.type in [_cmarkCmarkNodeType.CMARK_NODE_CODE_BLOCK.value]:
             del e.data
             del e.as_code.info
-            e.data = str()
-            e.as_code.info = str()
+            e.data = ''
+            e.as_code.info = ''
         elif e.type in [
                 _cmarkCmarkNodeType.CMARK_NODE_TEXT.value,
                 _cmarkCmarkNodeType.CMARK_NODE_HTML_INLINE.value,
@@ -113,23 +112,23 @@ def _cmark_S_free_nodes(e: _cmarkCmarkNode):
                 _cmarkCmarkNodeType.CMARK_NODE_HTML_BLOCK.value,
         ]:
             del e.data
-            e.data = str()
+            e.data = ''
         elif e.type in [
                 _cmarkCmarkNodeType.CMARK_NODE_LINK.value,
                 _cmarkCmarkNodeType.CMARK_NODE_IMAGE.value,
         ]:
             del e.as_link.url
             del e.as_link.title
-            e.as_link.url = str()
-            e.as_link.title = str()
+            e.as_link.url = ''
+            e.as_link.title = ''
         elif e.type in [
                 _cmarkCmarkNodeType.CMARK_NODE_CUSTOM_BLOCK.value,
                 _cmarkCmarkNodeType.CMARK_NODE_CUSTOM_INLINE.value,
         ]:
             del e.as_custom.on_enter
             del e.as_custom.on_exit
-            e.as_custom.on_enter = str()
-            e.as_custom.on_exit = str()
+            e.as_custom.on_enter = ''
+            e.as_custom.on_exit = ''
 
         if e.last_child:
             # Splice children into list
@@ -163,14 +162,14 @@ def _cmark_cmark_set_cstr(mem: _cmarkCmarkMem, dst: str, src: str) -> tuple:
         dst = copy.deepcopy(src[:length + 1])
     else:
         length = 0
-        dst = str()
+        dst = ''
 
     if old:
         # Alternative to:
         #     mem->free(old);
         del old
         del dst
-        dst = str()
+        dst = ''
 
     return length, dst
 
diff --git a/md_toc/cmark/node_h.py b/md_toc/cmark/node_h.py
index 2a4fe9d..b05af08 100644
--- a/md_toc/cmark/node_h.py
+++ b/md_toc/cmark/node_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # node_h.py
 #
diff --git a/md_toc/cmark/references_c.py b/md_toc/cmark/references_c.py
index 2c81ace..137af06 100644
--- a/md_toc/cmark/references_c.py
+++ b/md_toc/cmark/references_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # reference_c.py
 #
@@ -65,7 +64,7 @@ def _cmark_normalize_reference(mem: _cmarkCmarkMem,
         raise ValueError
 
     #     if result[0] == '\0':
-    if result == str():
+    if result == '':
         #     mem.free(result)
         del result
         return None
diff --git a/md_toc/cmark/references_h.py b/md_toc/cmark/references_h.py
index c24b4c4..e123163 100644
--- a/md_toc/cmark/references_h.py
+++ b/md_toc/cmark/references_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # reference_h.py
 #
diff --git a/md_toc/cmark/scanners_c.py b/md_toc/cmark/scanners_c.py
index f621642..b40d7c9 100644
--- a/md_toc/cmark/scanners_c.py
+++ b/md_toc/cmark/scanners_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # scanners_c.py
 #
diff --git a/md_toc/cmark/scanners_h.py b/md_toc/cmark/scanners_h.py
index 218bc76..e5306fc 100644
--- a/md_toc/cmark/scanners_h.py
+++ b/md_toc/cmark/scanners_h.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # scanners_h.py
 #
diff --git a/md_toc/cmark/utf8_c.py b/md_toc/cmark/utf8_c.py
index 5d75d76..e9a663f 100644
--- a/md_toc/cmark/utf8_c.py
+++ b/md_toc/cmark/utf8_c.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # utf8_c.py
 #
diff --git a/md_toc/constants.py b/md_toc/constants.py
index 76ceafc..232dda9 100644
--- a/md_toc/constants.py
+++ b/md_toc/constants.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # constants.py
 #
diff --git a/md_toc/exceptions.py b/md_toc/exceptions.py
index 22ee984..e646c93 100644
--- a/md_toc/exceptions.py
+++ b/md_toc/exceptions.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # exceptions.py
 #
diff --git a/md_toc/generic.py b/md_toc/generic.py
index 3008518..6371456 100644
--- a/md_toc/generic.py
+++ b/md_toc/generic.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # generic.py
 #
@@ -60,7 +59,7 @@ def _extract_lines(input_file: str, start: int, end: int) -> str:
     lines: list[str] = list()
     line_counter: int = 1
 
-    with open(input_file, 'r') as f:
+    with open(input_file) as f:
         line: str = f.readline()
         while line:
             if line_counter >= start and line_counter <= end:
@@ -100,7 +99,7 @@ def _get_existing_toc(filename: str, marker: str) -> tuple:
     )
     marker_line_positions_length: int = len(marker_line_positions)
 
-    old_toc: str = str()
+    old_toc: str = ''
     first_marker: int = 1
     second_marker: int = 2
     two_or_more_markers: bool = False
@@ -136,7 +135,7 @@ def _get_existing_toc(filename: str, marker: str) -> tuple:
                 old_toc = _extract_lines(filename, start_line,
                                          end_line).strip()
             else:
-                old_toc = str()
+                old_toc = ''
 
             lines_to_delete.append([
                 marker_line_positions[first_marker],
diff --git a/md_toc/tests/__init__.py b/md_toc/tests/__init__.py
index 0567b04..3a83b9d 100644
--- a/md_toc/tests/__init__.py
+++ b/md_toc/tests/__init__.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # __init__.py
 #
diff --git a/md_toc/tests/benchmark.py b/md_toc/tests/benchmark.py
index 94a5d24..8b2c956 100755
--- a/md_toc/tests/benchmark.py
+++ b/md_toc/tests/benchmark.py
@@ -1,5 +1,4 @@
 #!/usr/bin/env python3
-# -*- coding: utf-8 -*-
 #
 # Copyright (C) 2022 Franco Masotti (see /README.md)
 #
diff --git a/md_toc/tests/tests.py b/md_toc/tests/tests.py
index 1cdd376..1ae16f6 100644
--- a/md_toc/tests/tests.py
+++ b/md_toc/tests/tests.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # tests.py
 #
@@ -140,8 +139,8 @@ def test__extract_lines(self):
         r"""Test extracting lines between line intervals."""
         with open('foo.md', 'w') as f:
             f.write(CMARK_LINE_FOO)
-        self.assertEqual(generic._extract_lines('foo.md', 2, 2), str())
-        self.assertEqual(generic._extract_lines('foo.md', 1024, 2048), str())
+        self.assertEqual(generic._extract_lines('foo.md', 2, 2), '')
+        self.assertEqual(generic._extract_lines('foo.md', 1024, 2048), '')
         self.assertEqual(generic._extract_lines('foo.md', 1, 1),
                          CMARK_LINE_FOO)
 
@@ -197,7 +196,7 @@ def test__get_existing_toc(self):
         with open('foo.md', 'w') as f:
             f.write(H1 + S1 + CMARK_LINE_FOO)
         self.assertEqual(generic._get_existing_toc('foo.md', '<!--TOC-->'),
-                         (str(), list(), False, 0, dict(), 0))
+                         ('', list(), False, 0, dict(), 0))
 
         # 1 TOC marker: TOC == marker.
         with open('foo.md', 'w') as f:
@@ -238,23 +237,22 @@ def test__get_existing_toc(self):
                     MARKER + LINE_LINE_FEED + LINE_LINE_FEED + H1 + S1 +
                     CMARK_LINE_FOO)
         self.assertEqual(generic._get_existing_toc('foo.md', MARKER),
-                         (str(), list(), True, 1, {
+                         ('', list(), True, 1, {
                              1: 1,
                              2: 5
                          }, 1))
 
     def test__replace_substring(self):
         r"""Test that the string is replaced with another one between the two specified indices."""
-        self.assertEqual(generic._replace_substring(str(), str(), 0, 0), str())
-        self.assertEqual(generic._replace_substring(str(), str(), 1024, 1024),
-                         str())
-
-        self.assertEqual(
-            generic._replace_substring(str(), CMARK_LINE_FOO, 0, 0), str())
-        self.assertEqual(
-            generic._replace_substring(CMARK_LINE_FOO, str(), 0, 0), 'oo')
-        self.assertEqual(
-            generic._replace_substring(str(), CMARK_LINE_FOO, 0, 0), str())
+        self.assertEqual(generic._replace_substring('', '', 0, 0), '')
+        self.assertEqual(generic._replace_substring('', '', 1024, 1024), '')
+
+        self.assertEqual(generic._replace_substring('', CMARK_LINE_FOO, 0, 0),
+                         '')
+        self.assertEqual(generic._replace_substring(CMARK_LINE_FOO, '', 0, 0),
+                         'oo')
+        self.assertEqual(generic._replace_substring('', CMARK_LINE_FOO, 0, 0),
+                         '')
         # Replace first 'f' of 'foo' with 'foo' -> 'foo|oo'
         self.assertEqual(
             generic._replace_substring(CMARK_LINE_FOO, CMARK_LINE_FOO, 0, 0),
@@ -313,7 +311,7 @@ def test__replace_substring(self):
 
     def test__string_empty(self):
         r"""A string is empty if it contains whitespace characters, excluding consecutive sequences of \n\r."""
-        self.assertTrue(generic._string_empty(str()))
+        self.assertTrue(generic._string_empty(''))
         self.assertTrue(generic._string_empty('\u000a'))
         self.assertTrue(generic._string_empty('\u000d'))
         self.assertTrue(generic._string_empty('\u000b'))
@@ -335,7 +333,7 @@ def test__string_empty(self):
 
     def test__detect_toc_list(self):
         r"""Detect a markdown list generated by md-toc."""
-        self.assertFalse(generic._detect_toc_list(str()))
+        self.assertFalse(generic._detect_toc_list(''))
 
         # Unordered list.
         self.assertTrue(generic._detect_toc_list('- list'))
@@ -453,14 +451,14 @@ def test__detect_toc_list(self):
 
     def test__read_line_interval(self):
         r"""Extract a line interval."""
-        self.assertEqual(generic._read_line_interval(str(), 1, 1), str())
-        self.assertEqual(generic._read_line_interval(str(), 0, 1), str())
-        self.assertEqual(generic._read_line_interval(str(), 1, 0), str())
-        self.assertEqual(generic._read_line_interval(str(), 0, 0), str())
+        self.assertEqual(generic._read_line_interval('', 1, 1), '')
+        self.assertEqual(generic._read_line_interval('', 0, 1), '')
+        self.assertEqual(generic._read_line_interval('', 1, 0), '')
+        self.assertEqual(generic._read_line_interval('', 0, 0), '')
         self.assertEqual(generic._read_line_interval('a', 1, 1), 'a')
-        self.assertEqual(generic._read_line_interval('a', 0, 1), str())
-        self.assertEqual(generic._read_line_interval('a', 1, 0), str())
-        self.assertEqual(generic._read_line_interval('a', 0, 0), str())
+        self.assertEqual(generic._read_line_interval('a', 0, 1), '')
+        self.assertEqual(generic._read_line_interval('a', 1, 0), '')
+        self.assertEqual(generic._read_line_interval('a', 0, 0), '')
         self.assertEqual(generic._read_line_interval('a\u000da', 1, 1), 'a')
         self.assertEqual(generic._read_line_interval('a\u000da', 1, 2), 'aa')
         self.assertEqual(generic._read_line_interval('a\u000da', 2, 2), 'a')
@@ -476,7 +474,7 @@ def test__read_line_interval(self):
         self.assertEqual(generic._read_line_interval('ab\u000d\u000ac', 2, 2),
                          'c')
         self.assertEqual(
-            generic._read_line_interval('ab\u000d\u000a\u000ac', 2, 2), str())
+            generic._read_line_interval('ab\u000d\u000a\u000ac', 2, 2), '')
         self.assertEqual(
             generic._read_line_interval('ab\u000d\u000a\u000ac', 2, 3), 'c')
 
@@ -511,7 +509,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(lines, 'hello')
@@ -523,7 +521,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -537,7 +535,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(lines, 'hello' + '\n' + MARKER + MARKER)
@@ -550,7 +548,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -565,7 +563,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -580,7 +578,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -595,7 +593,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -610,7 +608,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -625,7 +623,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -640,7 +638,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -655,7 +653,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -670,7 +668,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -684,7 +682,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -698,7 +696,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -713,7 +711,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -728,7 +726,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -743,7 +741,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -758,7 +756,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -773,7 +771,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -788,7 +786,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -803,7 +801,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -818,7 +816,7 @@ def test_write_string_on_file_between_markers(self):
                                                  LINE,
                                                  MARKER,
                                                  newline_string='\n')
-        with open('foo.md', 'r') as f:
+        with open('foo.md') as f:
             lines = f.readlines()
         lines = ''.join(lines)
         self.assertEqual(
@@ -1317,11 +1315,10 @@ def test_build_toc_line(self):
     def test_filter_indices_from_line(self):
         r"""Test removing indices from a string."""
         self.assertEqual(api.filter_indices_from_line('foo', [range(0, 3)]),
-                         str())
-        self.assertEqual(api.filter_indices_from_line(str(), [range(0, 1024)]),
-                         str())
-        self.assertEqual(api.filter_indices_from_line(str(), [range(0, 0)]),
-                         str())
+                         '')
+        self.assertEqual(api.filter_indices_from_line('', [range(0, 1024)]),
+                         '')
+        self.assertEqual(api.filter_indices_from_line('', [range(0, 0)]), '')
         self.assertEqual(
             api.filter_indices_from_line(512 * '1', [range(0, 512 - 1)]), '1')
         self.assertEqual(api.filter_indices_from_line(512 * '1', []),
@@ -2406,11 +2403,11 @@ def test_remove_html_tags(self):
         # Example 632 [GFM 0.29.0.gfm.2].
         self.assertEqual(
             api.remove_html_tags('<a><bab><c2c>', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a><bab><c2c>', 'cmark'),
-            str(),
+            '',
         )
 
         # Example 585 [Commonmark 0.28].
@@ -2419,11 +2416,11 @@ def test_remove_html_tags(self):
         # Example 633 [GFM 0.29.0.gfm.2].
         self.assertEqual(
             api.remove_html_tags('<a/><b2/>', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a/><b2/>', 'cmark'),
-            str(),
+            '',
         )
 
         # Example 586 [Commonmark 0.28].
@@ -2433,41 +2430,41 @@ def test_remove_html_tags(self):
         # Original example with extensions.
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\ndata="foo" >', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\r\ndata="foo" >', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\rdata="foo" >', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\n\rdata="foo" >', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a\t/><b2\ndata="foo" >', 'github'),
-            str(),
+            '',
         )
         # Two newlines.
         self.assertEqual(
             api.remove_html_tags('<a\t\t  /><b2\n\ndata="foo" >', 'github'),
-            str(),
+            '',
         )
 
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\ndata="foo" >', 'cmark'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\r\ndata="foo" >', 'cmark'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\rdata="foo" >', 'cmark'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('<a  /><b2\n\rdata="foo" >', 'cmark'),
@@ -2475,7 +2472,7 @@ def test_remove_html_tags(self):
         )
         self.assertEqual(
             api.remove_html_tags('<a\t\t  /><b2\ndata="foo" >', 'cmark'),
-            str(),
+            '',
         )
         # Two newlines.
         self.assertEqual(
@@ -2491,13 +2488,13 @@ def test_remove_html_tags(self):
             api.remove_html_tags(
                 '<a foo="bar" bam = \'baz <em>"</em>\'\n_boolean zoop:33=zoop:33 />',
                 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags(
                 '<a foo="bar" bam = \'baz <em>"</em>\'\n_boolean zoop:33=zoop:33 />',
                 'cmark'),
-            str(),
+            '',
         )
 
         # Example 588 [Commonmark 0.28].
@@ -2586,11 +2583,11 @@ def test_remove_html_tags(self):
         # Example 642 [GFM 0.29.0.gfm.2].
         self.assertEqual(
             api.remove_html_tags('</a></foo >', 'github'),
-            str(),
+            '',
         )
         self.assertEqual(
             api.remove_html_tags('</a></foo >', 'cmark'),
-            str(),
+            '',
         )
 
         # Example 595 [Commonmark 0.28].
@@ -2830,8 +2827,7 @@ def test_replace_and_split_newlines(self):
                                            LINE_LINE_FEED + LINE_LINE_FEED +
                                            LINE_CARRIAGE_RETURN +
                                            LINE_LINE_FEED + CMARK_LINE_BAR),
-            [CMARK_LINE_FOO, str(),
-             str(), CMARK_LINE_BAR])
+            [CMARK_LINE_FOO, '', '', CMARK_LINE_BAR])
 
     def test_get_atx_heading(self):
         r"""Test the title gathering for edge cases and various parsers.
@@ -3959,7 +3955,7 @@ def test_get_md_header(self):
                        'header text trimmed': None,
                        'visible': False
                    }]):
-            with patch('md_toc.api.build_anchor_link', return_value=str()):
+            with patch('md_toc.api.build_anchor_link', return_value=''):
                 self.assertEqual(api.get_md_header(CMARK_LINE_FOO, dict(), 1),
                                  [None])
 
@@ -3972,7 +3968,7 @@ def test_get_md_header(self):
                        'header text trimmed': None,
                        'visible': True
                    }]):
-            with patch('md_toc.api.build_anchor_link', return_value=str()):
+            with patch('md_toc.api.build_anchor_link', return_value=''):
                 self.assertEqual(api.get_md_header(CMARK_LINE_FOO, dict(), 1),
                                  [None])
 
diff --git a/md_toc/types.py b/md_toc/types.py
index 4482d5a..2dd1d38 100644
--- a/md_toc/types.py
+++ b/md_toc/types.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # types.py
 #
diff --git a/setup.py b/setup.py
index ee9572c..cab8e40 100644
--- a/setup.py
+++ b/setup.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #
 # setup.py
 #