Comments Content
On this page:
Comments support the same rich content that Pages do.
Content Formatting Support
As such, anything you can put in a page, you can also put them in a comment. This includes tables, attachments, columns, panels, as well as issue mentions, page mentions, and user mentions.
Comment Content Limitation
The big limitation with comments is horizontal space. Because comments are shown underneath the page, they have a limited width of approximately 650 pixels. Effectively this means, some content (like images and tables) simply cannot be as wide as it could be in a page.
Addtionally, on Jira Data Center, pages support tasks, which cannot be placed in a comment.