'tel' is a URI scheme specification for telephone numbers, which describes resources for telephone numbers linked to within documents.
The tel URI scheme can be used to create a link to a telephone number on the web, which can be implemented by prepending the value tel: to a telephone number, and then placing the whole value into an a element's href attribute, like so:
<a href="tel:867-5309">Call Me</a>
Do not use this tag if your question refers to telephone numbers in general, such as using regular expressions to match a telephone number's format, or if you are referring to the tel attribute of an input element (use input instead).
