update advanced documentation with local PGM core docs

Signed-off-by: Martijn Govers <Martijn.Govers@Alliander.com>

Author: mgovers

docs/advanced_documentation/build-guide.md

@@ -477,11 +477,16 @@ The `pip install .` part of the command installs the complete package from scrat
 
 The C API documentation is generated using [Doxygen](https://www.doxygen.nl). If you do not have Doxygen installed, it can also be temporarily bypassed by commenting out the `breathe` settings in  `docs/conf.py`.
 
-The documentation can be built with the following commands, resulting in html files of the webpages which can be found in `docs/_build/html` directory.
+The documentation can be built with the following commands, resulting in HTML files of the webpages which can be found in `docs/_build/html` directory.
 
 ```shell
 cd docs/doxygen
 doxygen
 cd ..
 sphinx-build -b html . _build/html
 ```
+
+```{note}
+The user documentation generated by [Sphinx](https://github.com/sphinx-doc/sphinx) only contains the C API documentation.
+Doxygen, however, also builds the documentation for the Power Grid Model core implementation, which can be accessed after building the documentation locally via `docs/_build/html/index.html`.
+```

docs/advanced_documentation/core-design.md

@@ -48,3 +48,8 @@ graph TD
 
     ComponentsOutput -->|Output| Output(Output data)
 ```
+
+## Detailed Power Grid Model core design
+
+The sheer size and complexity of the Power Grid Model core implementation makes it hard to generate an up-to-date and comprehensive graph of its design.
+For a full overview of the core, it is recommended to build and access the Power Grid Model core documentation by following the steps in the [build guide](./build-guide.md#documentation).

docs/doxygen/Doxyfile

@@ -529,7 +529,7 @@ EXTRACT_LOCAL_CLASSES  = YES
 # included.
 # The default value is: NO.
 
-EXTRACT_LOCAL_METHODS  = NO
+EXTRACT_LOCAL_METHODS  = YES
 
 # If this flag is set to YES, the members of anonymous namespaces will be
 # extracted and appear in the documentation as a namespace called
@@ -868,7 +868,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = ../../power_grid_model_c/
+INPUT                  = "../../power_grid_model_c/" "../../src/" "../../tests/"
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses