Cover ignored blocks in Spec and FAQ

faq.md

@@ -113,6 +113,49 @@ testing.
 If you have an entire directory that you want to "exclude" from REUSE compliance
 testing, you can [use a DEP5 file](#bulk-license).
 
+## How do I exclude certain files from REUSE compliance testing? {#exclude-lines}
+
+In order to make the tool ignore a specific section containing strings that may
+falsely be detected as copyright or license statements, you can wrap it within
+the two comments `REUSE-IgnoreStart` and `REUSE-IgnoreEnd`.
+
+Please note that this must not be used to ignore valid copyright and licensing
+information by yourself or a third party. The ignore blocks must only be used
+for marking blocks that may trigger false-positive detections and errors.
+
+An example for a file that contains commands or documentation that confuse the
+REUSE helper tool:
+
+```
+# SPDX-FileCopyrightText: 2021 Jane Doe
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+echo "SPDX-FileCopyrightText: $(date +'%Y') John Doe" > file.txt
+echo "SPDX-License-Identifier: MIT" > file.txt
+```
+
+The tool would complain that it cannot parse the license in the last line and it
+would falsely understand the second-last line as an additional copyright holder:
+
+```
+reuse._util - ERROR - Could not parse 'MIT" > file.txt'
+reuse.project - ERROR - 'foobar.sh' holds an SPDX expression that cannot be parsed, skipping the file
+```
+
+This is how the section that causes these errors can be ignored:
+
+```
+# SPDX-FileCopyrightText: 2021 Jane Doe
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# REUSE-IgnoreStart
+echo "SPDX-FileCopyrightText: $(date +'%Y') John Doe" > file.txt
+echo "SPDX-License-Identifier: MIT" > file.txt
+# REUSE-IgnoreEnd
+```
+
 ## Do you support a version control system other than Git? {#no-git}
 
 Yes, the helper tool also supports [Mercurial](https://www.mercurial-scm.org/).

spec.md

@@ -129,6 +129,26 @@ An example of a comment header:
 # SPDX-License-Identifier: GPL-3.0-or-later
 ```
 
+If these tags are additionally used in the file without describing the file's
+actual license or copyright but for example as part of an output command or
+documentation, these occurences MAY be put between two comments:
+`REUSE-IgnoreStart` and `REUSE-IgnoreEnd`. The REUSE Tool then ignores all tags
+within. This technique MUST NOT be used to ignore valid tags for licensing or
+copyright.
+
+An example for an ignored block:
+
+```
+# SPDX-FileCopyrightText: 2021 Jane Doe
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# REUSE-IgnoreStart
+echo "SPDX-FileCopyrightText: $(date +'%Y') John Doe" > file.txt
+echo "SPDX-License-Identifier: MIT" > file.txt
+# REUSE-IgnoreEnd
+```
+
 ### DEP5
 
 Alternatively, Copyright and Licensing Information MAY be associated with a