That sounds like good advice. Like you say though, difficult to verify. Would you analyze the contents of the string, or the subject of the assignment? Something else?
Without a reliable way to verify the intention of a string, applying the same advice you give for tabs vs. spaces seems preferable - Pick one and use it consistently.
That advice would also prevent cowboy developers from creatively misinterpreting the difference between internal and external.
--- In firstname.lastname@example.org, "douglascrockford" <douglas@...> wrote:
> My advice is to use "double quotes" for strings that are meaningful externally, like urls, html templates, and error messages; and to use 'single quotes' for strings that are meaningful internally, like character constants, property names, and symbols.
> I have not discover an automatic way to verify usage.