Issue
Context changes - If an error occurs in the file picker the error modal does not announce to screen readers that a modal has been opened.
Guidance - Modal window is not being announced at all to screen reader users.

Standard Level
WCAG 2 3.3.2 (A) http://www.w3.org/WAI/WCAG20/quickref/#qr-minimize-error-cues
WCAG 2 4.1.2 (A) http://www.w3.org/WAI/WCAG20/quickref/#qr-ensure-compat-rsv

Impact
Serious
Critical

Example Link
http://demo.moodle.net/mod/assign/view.php?id=1778&action=editsubmission

Test Steps

1. Login as a student
2. Navigate to a course
3. Click the assignment
4. Click add submissions
5. Click the Private files button in the file picker with a screen reader on after a user has been logged out.
6. Notice nothing is announced to the screen reader when the error modal appears