case-insensitive string comparison

[Sam Steingold]

Hi,

Emacs Lisp has 3 ways to describe comparison that ignores case:

1. "ignore-case", as in, e.g., `member-ignore-case'
2. "case-fold", as in, e.g., `case-fold-search'
3. "case-insensitive", as in, e.g., 
`minibuffer-history-case-insensitive-variables'

Is there a general rule when to use which naming?

Specifically, I would like to add

--8<---------------cut here---------------start------------->8---
(defun string-equal-ignore-case (s1 s2)
  "Like `string-equal', but case-insensitive.
Upper-case and lower-case letters are treated as equal.
Unibyte strings are converted to multibyte for comparison."
  (eq t (compare-strings s1 0 nil s2 0 nil t)))
--8<---------------cut here---------------end--------------->8---

to subr.el next to `string-prefix-p' - is this okay?

Thanks.

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.2113
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