Rich-text is any kind of textual content that can have media, semantic or formatting features embedded.
There are many different uses for rich-text. It is common to see it when people attempt to freely write or communicate a message. The article you’re reading right now is rich-text, just like comments or chat inputs that can accept bold for styling words, for example.
The problem with rich-text is that all non-textual information present in it must be somehow described so it can be saved as an integral part of the text. The most common approach for this is using a markup language where such additional attributes are mixed inside the text.
Who cares?! What’s the problem with it?
Not taking into consideration the limitations imposed by some markup languages, the most important problem with this is interoperability.
The fact is that content produced by end-users of our systems can be used in different contexts, for many different purposes. For example: