“Id.” is Short for “Identifier”

As you can see, my OCD acts up when I see WordPress using uppercase “ID” in core function names, such as the get_the_ID() function.

“Id.” (note the period), as used here, is an abbreviation (contraction) of the word “identifier.” It is not an acronym, nor a “multi-word abbreviation” (i.e. for something like “Identity Document”), so it should not be all uppercase.

Also, according to WordPress’ own naming conventions, all function names should use lowercase letters and underscores for separating words.

Use lowercase letters in variable, action, and function names […]

And I wonder why I never get anything done …