diff --git a/README.rst b/README.rst
index 294d0ad..bd20570 100644
--- a/README.rst
+++ b/README.rst
@@ -306,17 +306,9 @@ A few things to notice:
 Multiple source files
 ---------------------
 
-Most projects have more than one source file and you can parse them all in one
-call. For example:
-
-.. code-block:: python
-
-    parsed = fp.parse(["source.txt", "other_source.txt"], , (AssigmentBlock, Equality))
-
-will produce a ``ParsedProject`` object with two elements.
-
-But in many cases, a file might refer to another that also need to be parsed
-(e.g. an `#include` statement in c). **flexparser** provides the ``IncludeStatement``
+Most projects have more than one source file internally connected.
+A file might refer to another that also need to be parsed (e.g. an
+`#include` statement in c). **flexparser** provides the ``IncludeStatement``
 base class specially for this purpose.
 
 .. code-block:: python
@@ -404,6 +396,41 @@ Explicit Block classes
 
     parsed = fp.parse("source.txt", EntryBlock)
 
+
+Customizing parsing
+-------------------
+
+In certain cases you might want to leave to the user some configuration
+details. We have method for that!. Instead of overriding ``from_string``
+override ``from_string_and_config``. The second argument is an object
+that can be given to the parser, which in turn will be passed to each
+``ParsedStatement`` class.
+
+.. code-block:: python
+
+    @dataclass(frozen=True)
+    class NumericAssigment(fp.ParsedStatement):
+        """Parses the following `this <- other`
+        """
+
+        lhs: str
+        rhs: numbers.Number
+
+        @classmethod
+        def from_string_and_config(cls, s, config):
+            if "==" not in s:
+                # This means: I do not know how to parse it
+                # try with another ParsedStatement class.
+                return None
+            lhs, rhs = s.split("==")
+            return cls(lhs.strip(), config.numeric_type(rhs.strip()))
+
+    class Config:
+
+        numeric_type = float
+
+    parsed = fp.parse("source.txt", NumericAssigment, Config)
+
 ----
 
 This project was started as a part of Pint_, the python units package.
diff --git a/flexparser/__init__.py b/flexparser/__init__.py
index 53c574c..4ea106b 100644
--- a/flexparser/__init__.py
+++ b/flexparser/__init__.py
@@ -2,9 +2,12 @@
     flexparser
     ~~~~~~~~~
 
-    Classes for persistent caching and invalidating cached objects,
-    which are built from a source object and a (potentially expensive)
-    conversion function.
+    Classes and functions to create parsers.
+
+    The idea is quite simple. You write a class for every type of content
+    (called here ``ParsedStatement``) you need to parse. Each class should
+    have a ``from_string`` constructor. We used extensively the ``typing``
+    module to make the output structure easy to use and less error prone.
 
     :copyright: 2022 by flexparser Authors, see AUTHORS for more details.
     :license: BSD, see LICENSE for more details.
diff --git a/flexparser/flexparser.py b/flexparser/flexparser.py
index 714aba1..c78cd95 100644
--- a/flexparser/flexparser.py
+++ b/flexparser/flexparser.py
@@ -2,12 +2,14 @@
     flexparser.flexparser
     ~~~~~~~~~~~~~~~~~~~~~
 
-    There are three type of
+    Classes and functions to create parsers.
 
-    - statements: single lines handled by the Definition.from_string method.
-    - line directives
-    - block directives:
+    The idea is quite simple. You write a class for every type of content
+    (called here ``ParsedStatement``) you need to parse. Each class should
+    have a ``from_string`` constructor. We used extensively the ``typing``
+    module to make the output structure easy to use and less error prone.
 
+    For more information, take a look at https://github.com/hgrecco/flexparser
 
     :copyright: 2022 by flexparser Authors, see AUTHORS for more details.
     :license: BSD, see LICENSE for more details.
@@ -1002,12 +1004,51 @@ def parse(
     spec: SpecT,
     config=None,
     *,
-    strip_spaces=True,
+    strip_spaces: bool = True,
     delimiters=None,
-    locator=default_locator,
-    prefer_resource_as_file=True,
+    locator: ty.Callable[[StrictLocationT, str], StrictLocationT] = default_locator,
+    prefer_resource_as_file: bool = True,
 ) -> ParsedProject:
-    """Parse sources into a ParsedProject."""
+    """Parse sources into a ParsedProject dictionary.
+
+    Parameters
+    ----------
+    entry_point
+        file or resource, given as (package_name, resource_name).
+    spec
+        specification of the content to parse. Can be one of the following things:
+        - Parser class.
+        - Block or ParsedStatement derived class.
+        - Iterable of Block or ParsedStatement derived class.
+        - RootBlock derived class.
+    config
+        a configuration object that will be passed to `from_string_and_config`
+        classmethod.
+    strip_spaces : bool
+        if True, spaces will be stripped for each statement before calling
+        ``from_string_and_config``.
+    delimiters : dict
+        Sepecify how the source file is split into statements (See below).
+    locator : Callable
+        function that takes the current location and a target of an IncludeStatement
+        and returns a new location.
+    prefer_resource_as_file : bool
+        if True, resources will try to be located in the filesystem if
+        available.
+
+
+    Delimiters dictionary
+    ---------------------
+        The delimiters are specified with the keys of the delimiters dict.
+    The dict files can be used to further customize the iterator. Each
+    consist of a tuple of two elements:
+      1. A value of the DelimiterMode to indicate what to do with the
+         delimiter string: skip it, attach keep it with previous or next string
+      2. A boolean indicating if parsing should stop after fiSBT
+         encountering this delimiter.
+
+
+    """
 
     if isinstance(spec, type) and issubclass(spec, Parser):
         CustomParser = spec