Plain Language Recommendations
When a page element receives focus, it must not result in
- a substantial change to the page,
- the opening of a pop-up/new window,
- an additional change of keyboard focus, or
- any other change that could confuse or disorient the user.
WCAG 2.0 Recommendations
Guideline 3.2: Predictable
Make web pages appear and operate in predictable ways.