"Hey, can anyone help me with this CSS validation error? Wait, let me get the exact message again."
*Fixes a typo buried deep in a string of comments hundreds of lines up from the nearest validation error.*
*Re-validates document to get the validation error message back.*
*The document passes and is declared valid CSS.*
"Wat"
Literally no change at all, and now the validation message is back.
And I solved it. Apparently, the order of multiplicands matters significantly in CSS (or at least to a validator).
calc(2 * 3lh) is invalid.
calc(3lh * 2) is valid.
Length times unit-less value is valid CSS, but unit-less value times length is not, according to the W3C CSS Validator. I wonder if it's using the rules for validating division, where the operand order matters, for validating multiplication, where it shouldn't.