When (re)generating the documentation from the sources and not using the, internally patched CGAL, doxygen version one gets messages about:
```
warning: ignoring unsupported tag 'EXTRACT_ALL_NO_DETAILED_IF_EMPTY'
```
By introducing the option `CGAL_EXTRACT_ALL_NO_DETAILED_IF_EMPTY` this doxygen setting can be steered
- option not supplied to cmake, will use as if specified `-DCGAL_EXTRACT_ALL_NO_DETAILED_IF_EMPTY=ON`
- option supplied to cmake as `-DCGAL_EXTRACT_ALL_NO_DETAILED_IF_EMPTY=ON` will write the line `EXTRACT_ALL_NO_DETAILED_IF_EMPTY = YES` in the doxygen configuration
- option supplied to cmake as `-DCGAL_EXTRACT_ALL_NO_DETAILED_IF_EMPTY=OFF` will write the line `#EXTRACT_ALL_NO_DETAILED_IF_EMPTY = NO` in the doxygen configuration, so just using the default setting of `NO` line could be omitted but it is better to have a placeholder
Currently the needed extra definitions for MathJax usage (i.e. `\newcommand` and `\def` commaonds) are distributed over the header file and in a number of source code files.
Doxygen has the possibility for a centralize this by means of the MATHJAX_CODEFILE configuration setting, this has been implemented.
Based on #3713 a number of problems were solved, but also some new issues introduced.
- BaseDoxyfile.h see to it that the CGALAdvancedBegin is in a detailed part, so be sure to terminate the brief part by an extra carriage return
- commands like \pre, \note read till the beginning of the next section but a \htmlonly is not seen as a section separator, so insert an extra carriage return
- some places missed an "Advanced" indicator, used the cgalAdvancedType here.
##Note
in Periodic_2_triangulation_2.h there appear to be a number of images that are a bit in thin air (Captions: "Insertion of a point on an edge." and "Insertion in a face."). Also just above these images theer are a number of functions that have documentation, but this is non-doxygen documentation and as such not seen by doxygen
Form the doxygen documentation:
Normally the contents between \htmlonly and \endhtmlonly is inserted as-is. When you want to insert a HTML
fragment that has block scope like a table or list which should appear outside <p>..</p>, this can lead to invalid
HTML. You can use \htmlonly[block] to make doxygen end the current paragraph and restart it after \endhtmlonly.