HTMLMarkupText

Ensures any HTML code (e.g. code examples) within the note text export as HTML entities rather than literal HTML code.

Thus a > character is exported as > so as to show as > on screen and not be parsed as HTML code.

You would use a non-default value of false for any note where you have included HTML mark-up that has already been HTML 'entified' in the note text (and so a > character in text is exported unchanged as > thus rendering as source code, etc.).

$HTMLMarkupText can be set via the Export Inspector's ▸ Export tab, 'Markup text' box.

Whereas HTMLQuoteHTML just looks at mark-up code such as HTML/XML/PHP/etc. in the note's source text, HTMLMarkupText considers other aspects of the note. For example, if you set HTMLMarkupText to false macros are not expanded, styles are ignored, quick links are not created and so forth. As the attribute title implies you have turned mark-up off and you're just passing out raw text into the HTML export template. Depending on the latter's mark-up you may or may not see un-marked-up text in your browser.

Thus the default setting of true is almost invariably the correct setting for this attribute.

The attribute also controls, or has a part in, several display-related export functions (quick lists, auto-headings, etc.).

Note that $AutomaticIndent separately controls quick list layout within a note text window without affecting HTML export processing on quick list markers.