[css-values-3] Make Oriol happy by not abusing range notation if mod()/rem(); also make it clear which zero is returned.

Author: tabatkins

css-values-4/Overview.bs

@@ -2670,8 +2670,11 @@ Stepped Value Functions: ''round()'', ''mod()'', and ''rem()''</h3>
 	if both arguments are positive or both are negative:
 	the value of the function is equal to the value of A
 	shifted by the integer multiple of B
-	that brings the value into the range [0, B)
-	(that is, possibly including zero, but excluding B itself).
+	that brings the value <dfn noexport>between zero and B</dfn>.
+	(Specifically, the range includes zero
+	and excludes B.
+	More specifically, if B is positive the range starts at 0⁺,
+	and if B is negative it starts at 0⁻.)
 
 	<div class=example>
 		For example, ''mod(18px, 5px)'' resolves to the value ''3px'',
@@ -2689,12 +2692,12 @@ Stepped Value Functions: ''round()'', ''mod()'', and ''rem()''</h3>
 	are on opposite sides of zero:
 	''mod()'' (short for “modulus”)
 	continues to choose the integer multiple of B
-	that puts the value into the [0, B) range
+	that puts the value [=between zero and B=], as above
 	(guaranteeing that the result will either be zero
 	or share the sign of B, not A),
 	while ''rem()'' (short for "remainder")
 	chooses the integer multiple of B
-	that brings the value into the range [0, -B),
+	that puts the value [=between zero and B|between zero and -B=],
 	avoiding changing the sign of the value.
 
 	<div class=example>