We frequently use a number of tables in many of our documents, and it is often necessary to provide in definitions of the headers to help readers understand the content to read, inserted or updated. I have found a few ways to accomplish this:
Create a narrative above or below the table, which takes space depending upon complexity of the table
Create a link in the header name to some location in the document, but that takes the reader way and there isn't a clean way to jump back where yo came from (that i know of)
Create a link in the header name to an external document, which I still would do if the content is complex or has a long list of acceptable values.
When working on web sites with tables, i often provide hover buttons such as :information that contains a brief description of the column so i don't have to take the reader from the page. For more complex, then we pop up a side bar.
I think it wold be helpful if one could either have a special set of icons (like the message posts), but placed in line with text with some symbol :information, :questionmark, etc. Or possibly make the emojis have the option of containing a message when placed in the document.