Headings are usually indicated by increasing the font size, font weight, or the space around the title, but these visual differences may not be apparent to a person using Assistive Technologies. When the document is ‘strongly structured’ (the document uses grouping elements such as ‘Art’, ‘Sect’, and ‘Div’ to represent the organization of the material) and the heading is always and only the first child of the grouping element, then use ‘H’ on the FO for the heading. When the document is not strongly structured, use the ‘H1’ to ‘H6’ Structure Elements to indicate heading levels.
When generating PDF/UA:
Heading levels beyond ‘H6’ are allowed: for example, ‘H7’, and so on.
A document may use either only ‘H’ Structure Elements or only ‘H1’ to ‘H6’ Structure Elements (and beyond).
When using numbered heading levels:
The first heading must be ‘H1’.
More than one instance of any heading level may be used.
There cannot be gaps in the descending heading level sequence: for example, ‘H1’ then ‘H2’ then ‘H3’ is a valid sequence, but ‘H1’ then ‘H3’ is not.
The heading level sequence can increment without restarting at ‘H1’ if that reflects the document structure. For example, ‘H1’, ‘H2’, ‘H3’, ‘H2’, ‘H3’, ‘H4’, ‘H3’ is a valid sequence.