ithe first statement is NOT always true, especially for Microsoft Office products (Word, Outlook) even Windows text box dialogs./i
As a developer, this always drives me nuts. I expect a text box to treat underscores and dashes like my IDEs treat them: an underscore as a letter, and a dash as “punctuation”. In programming of course, this makes sense. An underscore is not an “operator” in the context of many (most?) common programming languages, unlike the dash (minus), or whitespace (symbol separator).
However, an underscore really has no official place in the English language. It was created for the typewriter, as a way of underlining. It’s word-separation usage only came with the advent of 2GLs. So confusion is understandable, if not really acceptable, when dealing with word-processing functionality.
At any rate, it would be nice if everyone treated it the same way. At least within a given context.