I've found it hard to discover the source or meaning of the unicode characters in the mode-line. All questions I've found referencing them are about how to get them to display correctly --- e.g. this question refers to the same characters I'm talking about.
What are these characters? What information do they convey? Where are they set, and how would I configure them if I decided to?
I was able to find documentation for these symbols here, in the spacemacs github README (where they belong).
The symbols show the modes that are active for the buffer, and correspond to the keys used to enable those modes. That's pretty useful.
Further, you can see what modes are represented by what characters simply by mousing over the character.
Specifically, spacemacs is using the Diminish minor mode to produce the characters in the mode-line.
All in all, this feature is well documented and also really easily discoverable. But I'm leaving an answer here in case anyone else is confused similarly.
