Link to issue number:

Fixes #3156. Strictly speaking, that issue covers other problems as well, but this addresses the issue for which it was originally opened. Other issues should be (re)opened for any remaining problems.

Summary of the issue:

When editing text, there is an insertion point at the end of a line. This is where you are positioned when you press the end key. Firefox also allows you to reach this position with the left/right arrow keys. When text wraps across multiple lines, lines other than the last have this insertion point, but it does not have its own IAccessible2 offset, since it doesn't actually exist in the text. Instead, the caret offset reported is the same offset as the start of the next line.

This is problematic for NVDA because when the user is at this position, NVDA reports the character at the start of the next line. Worse, it reports the next word and line instead of the current word and line.

Description of user facing changes

In Mozilla Firefox, NVDA now correctly reports the current character, word and line when the cursor is at the insertion point at the end of a line.

Description of development approach

IAccessible2 provides IA2_TEXT_OFFSET_CARET to deal with this. While somewhat awkward, the idea is that you pass this special offset to IAccessibleText functions so that they know you care about the caret and can handle it specially if the caret is at the end of line insertion point. For example, asking for the character at the caret might report (3, 3, None), where 3 is the caret offset. In contrast, if the caret was at the start of the next line, it might report (3, 4, 'c'). Similarly, asking for the line at the caret when at the end of the line might report (0, 3, 'ab ') instead of (3, 6, 'cd ') at the start of the next.

Unfortunately, making NVDA use IA2_TEXT_OFFSET_CARET when fetching units is tricky. IA2TextTextInfo would need to keep track of the fact that it was constructed for the caret and pass IA2_TEXT_OFFSET_CARET if so. But this means that when the caret moves, the TextInfo moves too, which breaks detaching the review cursor from the caret, etc.

Instead, a flag _isEndOfLineInsertionPoint has been added to MozillaCompoundTextInfo. This is set by querying the character at IA2_TEXT_OFFSET_CARET when constructing with POSITION_CARET. This allows us to implement special behaviour when this is True: we expand to no character, we expand to the current word/line instead of the next word/line, etc. If the TextInfo is copied, this flag is copied too. If the TextInfo is mutated in any way, the flag is set to False. This allows us to represent this position (even across copies) without being attached to the current position of the caret.

Some of this could theoretically be done in IA2TextTextInfo, but that would have meant plumbing (and coupling) this special casing through both classes. I'm not aware of any other implementation which supports IA2_TEXT_OFFSET_CARET that doesn't use MozillaCompoundTextInfo.

Note that although Chromium supports IA2_TEXT_OFFSET_CARET, it doesn't special case the insertion point at the end of a line. Thus, although this works fine in Chromium, there is no benefit there, though Chromium could choose to implement this to gain that benefit.

Testing strategy:

Test case:
data:text/html,<textarea cols="2">ab cd</textarea>

In Firefox:

1. Open the test case and focus the textarea.
2. Press end.
   • Incorrect result before this PR: "c"
   • Correct result after this PR: "blank"
3. Press read current line.
   • Incorrect result before this PR: "cd"
   • Correct result after this PR: "ab"
4. Press right arrow.
   • Observe: "c"
5. Press read current line.
   • Observe: "cd"

In Google Chrome:

1. Open the test case and focus the textarea.
2. Press end.
   • Incorrect result (before and after this PR): "c"
3. Press read current line.
   • Correct result (before and after this PR): "ab"
   • Note that Chromium does this by returning the current line for the real offset if the caret is positioned at the insertion point at the end of a line. However, this causes other problems; e.g. you are unable to move the review cursor to the next line if the caret is at this position.

Known issues with pull request:

None.

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.

Summary by CodeRabbit

• New Features

  • NVDA in Mozilla Firefox now accurately reports the current character, word, and line when the cursor is at the end of a wrapped line.

• Documentation

  • Updated user documentation to reflect the new enhancement in text reporting for Mozilla Firefox.