I installed BBCodePlus https://github.com/mantisbt-plugins/BBC ... ster-2.0.x plug-in in my mantis installation, and it works on text areas just fine. I can manually do [ b]some text[ /b] etc and it will show me bold/italic etc.
Note from the Github README:
"NOTE: This plugin does NOT interact well with the Markdown Processing feature of the Mantis Formatting plugin. Disabling the functionality is advised."
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