Expressions: accept a decimal comma outside parentheses (#1347) (#1382)

"2,5 mm" is 2.5 mm; inside a function's parentheses the comma still separates the arguments. Noted under design format 22: an expression typed with a decimal comma is saved as typed, so 0.12.0 asks for an update instead of failing to evaluate it.

docs/book/src/guide/parameters.md

@@ -17,7 +17,9 @@ does not also submit the parameter.
 
 Expressions are unit-aware: `2 * width + 5 mm`, `angle / 2`, `sqrt(area)`, `1 in + 3 mm`, using
 `+ - * / ^`, parentheses, `sin cos tan asin acos atan atan2 sqrt abs min max floor ceil round mod
-trunc` and unit conversion. A length where an angle is expected (or the other way round) is an
+trunc` and unit conversion. A decimal comma works too, outside parentheses: `2,5 mm` is
+`2.5 mm` (inside a function's parentheses the comma separates its arguments, so write
+`max(2.5, 3)` there). A length where an angle is expected (or the other way round) is an
 error, not a silent conversion. Cycles are reported with their path (`a → b → a`), renaming a
 parameter updates every expression, dimension and feature input that uses it, and a parameter
 in use can't be deleted (the error lists its users).