Understanding the @return Directive in Sass Function

The @return directive is an essential part of a Sass function in styling web pages. The main role of the @return directive in a Sass function is to call the return value of the function. It allows the function to send back (or "return") a result value after executing its code.

A typical Sass function makes use of the @return directive to generate a meaningful output after it does its job. Let's consider the following simple example of a Sass function:

@function square($num) {
  @return $num * $num;
}
body {
  width: square(4) * 1px;  // Output: body { width: 16px; }
}

In the above Sass function square($num), the @return directive tells Sass to take the value of variable $num, square it, and use the result as the return value of the function. In our CSS, when we call square(4), it returns 16, which is then used as the value of width property.

The @return directive is critical to creating robust, meaningful Sass functions. Without it, the function would not be able to contribute to the CSS output. The @return directive also aids in keeping your code DRY (Don't Repeat Yourself) by allowing you to reuse logic instead of rewriting the same pieces of code again and again.

In summary, the @return directive plays an integral role in Sass's function, which helps software developers write efficient, clear, and maintainable CSS code. It doesn't define a mixin or include the mixin in the document, nor does it have any direct relationship with displaying SassScript expression values as errors.