The menu element allows to specify a menu which is specific to a given document type.
Excerpts from rng_section_config/common.incl (same file for all variants):
<menu label="Se_ction">
<menu label="C_olumn" name="tableColumnMenu">
<item label="_Insert Before"
icon="xxe-config:common/icons/insertColumnBefore.png"
command="sect.tableEdit" parameter="insertColumnBefore"/>
<item label="I_nsert After"
icon="xxe-config:common/icons/insertColumnAfter.png"
command="sect.tableEdit" parameter="insertColumnAfter"/>
...
</menu>
<separator />
<item label="_Convert to HTML"
icon="xxe-config:common/mime_types/html.png"
command="sect.convertToHTML" />
</menu>A menu element has item, menu and separator child elements, each menu item invoking a command. A menu element is required to have a label attribute. In the value of the label attribute, character underscore ('_') may be used to specify the mnemonic of a menu or an item.