Less supports many handy built-in functions. A built-in function can be used to manipulate Less values inside mixins and set the variables' values. Last but not least, they can also be used in guard expressions. You will find the complete list of functions by visiting http://lesscss.org/functions/.
In this chapter, you won't find them all, but you will learn how to use functions from all different groups. Functions can be grouped based on their input and output types, where these types are mathematical functions, color functions, list functions, string functions, and type functions. There is also a small number of functions that can't be grouped using the preceding classification.