# with the addition that a leading '+' sign is ok. Note that leading zeros
# are fine, and will be left in the input, which is useful for things like
# phone numbers when you know that they are integers (the HTML5 type=tel
# with the addition that a leading '+' sign is ok. Note that leading zeros
# are fine, and will be left in the input, which is useful for things like
# phone numbers when you know that they are integers (the HTML5 type=tel