We need to clarify in help, what "Heading" is meant that appears in different places. See bug 137273 which shows user confusion because of misunderstanding this concept.
"Cross-references" help article  mentions it without any explanation:
> Headings The Selection box shows a list of all headings in the order of
> their appearance in the document.
We need to clarify that "Heading" for writer is any paragraph which has Outline level other than Text Body (with a reference to the corresponding paragraph property tab); and that *by default*, Heading N paragraph styles have that property set accordingly. That would give required technical background, and hint that the default setting may be changed, thus changing the behaviour of the field function.
"Index" help article  mentions outline levels; still, a direct reference to the corresponding paragraph property would help, and also addition that the paragraph styles are only added *when their outline levels are set, which is true by default*.
There may be other places that could benefit from this clarification.
This article also does not describe what "Outline" means.
> Assigns an outline level from 1 to 10 to the selected paragraphs or
> Paragraph Style. Select Text Body to reset the outline level.
No mention why would anyone want to change "outline level", and what would it affect.
"Chapter Numbering" feature is tightly connected here.
Bug 107573 had renamed the old "Outline Numbering" into "Chapter Numbering". That broke linguistical connection between the Outline Level property and the feature.
We need to describe, that it's this feature that creates the default assignment of Outline Levels to pre-defined Heading N paragraph styles. Also we need to clarify that this feature makes the level fixed for the chosen paragraph style (i.e., it cannot be modified in paragraph style dialog), and when a style is unassigned in Chapter Numbering, that style looses the outline level.