What are the links/tags/bookmarks starting with "E" in vim's help docs?

Question

In Vim's :help, there are many links/tags/bookmarks starting with E. For example, typing :help E355 takes you to a list of all of Vim's options. But there are hundreds of "E" style links/tags/bookmars. What are they, and why are they in the format "E" + number?

Answer 1

They are error tags. From 02.8 Finding help

If you see an error message that you don't understand, for example:

    E37: No write since last change (use ! to override) 

You can use the error ID at the start to find help about it:

    :help E37