This is the CKEditor 5 autoformatting feature.

Use Markdown syntax shortcodes to format content on the go. For example:

• Type _ around some text to make it italics.
• Type __ around some text to make it bold.
• Start a line with 1. followed by a space to create an ordered list.
• Start a line with - followed by a space to create an unordered list.
• Start a line with ˋˋˋ to create a code block.