Headings in a formatted text are extracted based on its outstanding font style or size, and placement above paragraph texts. The heading levels are differentiated mostly by font size. Headings with smaller font size categorized as having higher heading levels, hence those are lower in the content hierarchy.
The following headings are removed:
The first unique heading levels, like page title and author.
Those headings, that have too many instances on a page, see Limitations.
Headings are generated as styles, and the heading level paragraph property is extracted from these heading styles in case of DOCX and RTF conversions.
Headings are created as styles, named from Heading 1 to Heading N, and the number postfix is taken as the level.
Only DOCX and RTF formats support heading levels, EPUB and HTML formats support headings without heading levels.
You can view Navigation pane by pressing CTRL+F. Clicking Headings brings up available headings, indented by their levels. This pane allows easy navigation in a large document by clicking on the heading level.
You can set the heading level through Paragraph dialog box, by either right clicking on text, or selecting the proper heading style. This heading level property is being set through style, not through direct format. As a consequence if you change the level to 3 or higher via Style paragraph property, all these levels change.
You can create TOC with Microsoft Word. Move the pointer where the TOC needs to be placed, then click in the menuand choose the preferred TOC type. Microsoft Word automatically generates the belonging metadata, like hidden bookmarks.
You can overview heading levels, and correct the heading level of a paragraph in Microsoft Word, by clicking the menu. In this view you can reorder blocks of text vertically and horizontally by dragging the circle on the left side of the block. Blocks are derived from heading levels.
In order to keep the overall number of headings manageable, certain limitations are introduced:
Too many occurrences in a document:
Heading level are excluded if headings at that level appear:
on more than 10 instances on at least one page, or
at least twice on the majority of the pages
Short documents are limited by the number of heading levels:
The maximum heading level is a 2-based logarithm of the number of pages + 1. Any further heading levels below these heading level limits are removed. The thresholds may change in future.
Numbered headings avoid this limitation.