accessibility standards

Is there a standard for keyboard activation of drop-down menus? We are using multiple drop-down menus from various sources which behave differently from one another. Technically speaking, each individual jump menu is WCAG 2.0 AA accessible because it can be navigated keyboard-only, but the technique for opening the menu varies from menu to menu.

I can't imagine that to be a pleasant experience for site visitors, but I also can't seem to find documentation from an authoritative source for a standard menu-open behavior that could (theoretically) be applied across all drop-down menus.

Is there a standard? Where is it documented? If there is no standard, is there a way to force a single behavior across incompatible drop-downs or else enable forgiving actions? If not, is there a reasonable way, e.g., through appropriate ARIA labeling, to communicate the correct way to access a particular drop-down menu without forcing the site visitor to figure it out for themselves?

I despair of keyboard-only visitors being able to achieve mastery of drop-down menus on websites.

Details follow:

How many aspects of Drupal conform with the W3C's Authoring Tool Accessibility Guidelines (ATAG 2.0)?

If we can write each of those aspects up, we can help the Authoring Tool Accessibility Working Group (AUWG) of the W3C's Web Accessibility Initiative improve two important documents.

And while we're doing that, we can make it easier for Drupal themers and developers to understand what they can do—or, in some cases, must do—to ensure that Drupal remains accessible and continues to help people who use it create websites that are themselves accessible.

This post is not yet complete. Check back in a few hours. Or perhaps even tomorrow.