Purpose of tiny frames with invisible text after section headings

I’ve got an odt file (not written by me) in which there are tiny frames with invisible text after section headings (and also after table and figure titles). When I type Ctrl-A in such a frame (to select all) and copy the text, I get the section number followed by “.0” (e.g. “3.5.2.0”). When I double-click inside the frame, I get a dialog box “Edit Fields” with information like

  • Type: Number range
  • Select: Subclause
  • Format: Arabic (1 2 3)
  • Value: 0

What is the purpose of these frames?

I could not find any information. So I’ve asked both Mistral Le Chat and ChatGPT, which suggest that this is either for cross-referencing anchors or automatic numbering (but could not find any documentation). However, automatic numbering works without such frames, and if I remove such a frame, linking to the corresponding section still works.

The main issue with these frames is that when line numbering is active, I get a “1” on the left of each frame (as frames have their own line numbering), i.e. which appears over the section heading.