The mul tag accepts two parameters and returns as its output the value obtained after multiplying them.
The parameters may be literal strings, variables or output of other tags.
<cms:mul my_count '5' />
The snippet multiplies by 5 whatever value is contained within my_count variable and outputs the resulting value.
The tag expects two parameters as the values to be multiplied.
This tag is a self-closing one and does not set any variables of its own.