This is an attempt to normalize/formalize command summaries.
Main actions performed:
* Starts with the continuation of the phrase "The XXXX command, when called, ..." for user commands.
* Starts with "An internal command...", "A container command...", etc... when applicable.
* Always uses periods.
* Refrains from referring to other commands. If this is needed, backquotes should be used for command names.
* Tries to be very clear about the data type when applicable.
* Tries to mention additional effects, e.g. "The key is created if it doesn't exist" and "The set is deleted if the last member is removed."
* Prefers being terse over verbose.
* Tries to be consistent.