In December 2015, PHP 7 introduced scalar type declarations and with it the strict_types flag. This flag can be used to enforce the type of value passed to functions. Although I have seen it in action in the past, I have never actually used it before so I decided to look into it a little to see what it was about.
For some background, types are not strictly enforced in PHP. This means that it is not only possible to swap the type of a variable from one type to another, but it is also possible to swap a variable of one type to another depending on the context being used. Programmers getting started in PHP will spot this when attempting to print out a boolean value as this will be cast to an integer before being printed out. This means that when attempting to print 'true' PHP will instead print out '1'. PHP will automatically coerces values to be one type to another when passing values to functions.