The multiline accessor property of RegExp instances returns whether or not the m flag is used with this regular expression.
Description
RegExp.prototype.multiline has the value true if the m flag was used; otherwise, false. The m flag indicates that a multiline input string should be treated as multiple lines. For example, if m is used, ^ and $ change from matching at only the start or end of the entire string to the start or end of any line within the string.
The set accessor of multiline is undefined. You cannot change this property directly.
Examples
Using multiline
const regex = /foo/m;
console.log(regex.multiline); // true