Version 5.23.0

### Bug fixes

Presentation-related elements DOM elements are now marked as such to help screen readers.

[markdown mode](http://codemirror.net/mode/markdown/): Be more picky about what HTML tags look like to avoid false positives.

### New features

`findModeByMIME` now understands `+json` and `+xml` MIME suffixes.

[closebrackets addon](http://codemirror.net/doc/manual.html#addon_closebrackets): Add support for an `override` option to ignore language-specific defaults.

[panel addon](http://codemirror.net/doc/manual.html#addon_panel): Add a `stable` option that auto-scrolls the content to keep it in the same place when inserting/removing a panel.
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