From `perldoc perlre`: > A single "/x" tells the regular expression parser to ignore most whitespace that is neither backslashed nor within a bracketed charact

From `perldoc perlre`: > A single "/x" tells the regular expression parser to ignore most whitespace that is neither backslashed nor within a bracketed character class, nor within the characters of a multi-character metapattern like "(?i: ... )". You can use this to break up your regular expression into more readable parts. Also, the "#" character is treated as a metacharacter introducing a comment that runs up to the pattern's closing delimiter, or to the end of the current line if the pattern extends onto the next line.