s/  / /g;
Would be better written as
s/ +/ /g; (or, to treat all whitespace the same: s/\s+/ /g;)
since eight spaces would be converted to four using the first example, but the second would convert it to one space. The OP also isn't likely to want to s/, /,/g; since that would change text regardless of whether it's in an html tag or outside.