Regular expressions are a way to precisely specify a certain format for text. You can read more about regular expressions here. Surge uses the Ruby language's regular expressions engine to power this feature.

Note, on Surge, regular expressions must match the entire text. For example, the regular expression [0-9]+ will match 1234, but it will not match 1234a, because the expression doesn't capture the entirety of the text.

Below are some examples of how to use regular expressions to specify a specific format for text.

• A numerical value: [0-9]+.
• An email address: ^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\\.[a-zA-Z0-9-.]+. Note that this is not perfect, but should filter out many invalid email addresses and accept most valid ones.
• A range (i.e., a number, followed by a hyphen, followed by a number): '[0-9]+-[0-9]+'.
• Time of day in "HH:MM" format: [0-2][0-9]:[0-5][0-9].
• At most 280 characters: .{,280}.
• Text must contain the word "blue": .*blue.*.
• At least three lines: .*\\n.*\\n.*.