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Recipe 4.3 shows how to validate international phone numbers.
New area codes that fit the rules listed earlier are made available regularly, and even if a phone number is valid, that doesn’t necessarily mean it was issued or is in active use.
This includes the United States and its territories, Canada, Bermuda, and 16 Caribbean nations.
It excludes Mexico and the Central American nations.
Note that although this recipe claims to handle North American phone numbers, it’s actually designed to work with (NANP) numbers.
The NANP is the telephone numbering plan for the countries that share the country code “1”.
To allow matching phone numbers that omit the local area code, enclose the first group of digits together with its surrounding parentheses and following separator in an optional, noncapturing group: , with an empty set of parentheses.
To work around this, add code outside the regex that checks whether group 1 matched any text, and adjust the replacement text accordingly.The first group can optionally be enclosed with parentheses, and the first two groups can optionally be followed with a choice of three separators (a hyphen, dot, or space). It’s important that the hyphen appears first in this character class, because if it appeared between other characters, it would create a range, as with .The following layout breaks the regular expression into its individual parts, omitting the redundant groups of digits: ^ # Assert position at the beginning of the string. Any quantifier that allows something to be repeated zero times effectively makes that element optional.Two simple changes allow the previous regular expression to match phone numbers within longer text: matches the position between a word character and either a nonword character or the beginning or end of the text.Letters, numbers, and underscore are all considered word characters (see Recipe 2.6).The “1” in this pattern is preceded by an optional plus sign, and optionally followed by one of three separators (hyphen, dot, or space).