Error text not read by screen readers in Atto and filemanager

Error text displayed in Moodle is not consistently being automatically read by a screen reader. In some instances, error text is automatically read; while in other instances the text must be manually navigated to in order to be read, or cannot be read at all.

Examples:

1. When editing a page, attempting to submit while the name field is blank results in an error stating "You must supply a value here" - screen reader focus is automatically set to the field and the error is automatically announced.
2. When attempting to submit an assignment without adding a file to submit the error "Nothing was submitted" appears - this error is not automatically read by a screen reader, and must be manually navigated to in order to be read.
3. When submitting a blank .txt or Word file the error "The file 'zzz.txt' is either empty or a folder. To upload folders unzip them first" appears - this error is not automatically read by a screen reader and cannot be manually navigated to.
4. When attempting to submit a document using the add image control in Atto, the error that appears has its focus automatically set but is only read as "error close dialog" by the screen reader.

Tested Using: Windows 10 Professional, JAWS 17.0.1214, NVDA 2015.3, Firefox 43 Beta 5, Internet Explorer 11

Thanks to Morgan Felty and Oklahoma City Community College for bringing this issue to the MCAG's attention.