JEditor is a rich text editor for JIRA that produces clean, standards-compliant HTML code. This means that you can write some text in the editing area and format it in a few simple clicks of the toolbar buttons without knowing the ins and outs of the HTML syntax.
If at any time you would like to check the HTML source code of your document, use the Source toolbar button. The text that will appear in the editing area contains all the relevant HTML tags and attributes.
Since the source code view is not read-only, you can also edit your document while in this mode. To return to the default, WYSIWYG view, press the Source button again.
Do remember though that HTML editing is an advanced feature and its use should be limited to users with knowledge of the HTML markup language. JEditor lets you format your document or insert media like images or links without worrying about the source code and tags.