#40: added a warning to x-breakpoints
#41: added IE8 support to x-opacity
#42: changed default value from 1 to 0 for x-opacity
#39: fixed a potential issues with strings being used in place of lengths
#38: improved condition in x-rem
#44: simplified output in x-multiple-colored-gradient
#43: used an arglist instead of a list in x-multiple-colored-gradient
#45: simplified repeated condition in x-multiple-colored-gradient