Improve the examples given in PDF9

[DuffJohnson]

PDF9 includes the following:

Heading markup can be used:

• to indicate start of main content;
• to mark up section headings within the main content area;
• to demarcate different navigational sections, such as top or main navigation, left or secondary navigation, and footer navigation;
• to mark up images (containing text) which have the appearance of headings visually.

However, in the PDF context (the technology to which this technique applies)...

• the 1st bullet is dubious at best (especially if H1 is used for the document's title), as many documents locate front-matter (which isn't "main content") after the title.
• the 2nd bullet would ideally be enhanced to read: "to mark up section headings (text or images) within the main content area;"
• the 3rd bullet is simply inapplicable in the PDF context, and should be removed
• the 4th bullet can be retired based on the suggested change to the 2nd bullet.

Ironically, the given examples are far more applicable to HTML content than to PDF... but the various techniques applicable to HTML don't provide these examples.