Meaning of Purple Dashed Line without Arrow in Doxygen Collaboration Diagram for Groups?

Question

When creating a Collaboration Diagram in Doxygen that specifies the connections between Doxygen groups, what is the meaning of a purple dashed line without an arrow?

This option does not exist in the Doxygen documentation, the most similar option is a purple dashed line with an arrow, which is according to Doxygen documentation:

A purple dashed arrow indicated a "usage" relation, the edge of the arrow is labeled with the variable(s) responsible for the relation. Class A uses class B, if class A has a member variable m of type C, where B is a subtype of C (e.g. C could be B, B, T).

The documentation: https://www.doxygen.nl/manual/diagrams.html

I've created a Doxygen Collaboration Diagram by adding the argument GENERATE_HTML = YES. Also important to note that my code contains Doxygen groups. Here is the diagram I received:

Doxygen Collaboration graph with purple dashed line

The diagram describes the relations between the Doxygen groups I created. It contains a purple dashed line without an arrow, this option does not exist in the Doxygen documentation.

So the question is - what does it mean when there's no arrow in the purple dashed line? Is it the same but without a usage direction?

Answer 1

Not an answer, but a bit long for a comment. When looking at the grouping doxygen example and doing some standalone tests (and setting HAVE_DOT=YES) we see in the code:

/** @ingroup group1 group2 group3 group4
 *  namespace N1 is in four groups
 *  @sa @link group1 The first group@endlink, group2, group3, group4
 *
 *  Also see @ref mypage2
 */
namespace N1 {};

and in the documentation of the \ingroup command:

If the \ingroup command is placed in a comment block of a compound entity (like class, file or namespace), then it will be added to the group(s) identified by the <groupname>(s).

In other words the namespace N1 is part of the the different groups and this is a sort of usage relation between the different groups "through" the namespace N1