"aria-labelledby" for navigation panel entries and corresponding ids contain illegal whitespaces

In the navigation sidebar, for every list item an "aria-labelledby" attribute and associated "id " is automatically generated to improve accessibility. Both attributes must match. The entries are finally named in the form "document:subwikiname:path.to.page.Webhome_anchor".Spaces are also included, but are interpreted as separators for "aria-labelledby" see w3 documentation([https://www.w3.org/WAI/GL/wiki/Using_aria-labelledby_to_provide_a_name_for_user_interface_controls#Example_3. Because of this, for example, the WAVE tool correctly throws a "Broken ARIA reference" error. The spaces should be replaced appropriately in the "id" and "aria-labelledby" attributes.

We are keen to work on this, but really struggle to find the location in the source code, where the attributes are generated. We appreciate any hints.