Reference: attributes

id attribute

Identifier

id
Type	Element	Description	Use
ID	most elements	assigns a unique identifier name to an element	To assign a unique identifier name to an element. The name must be unique within the document.

An id name must begin with a letter (A-Z, a-z) and may be followed by any number of letters, digits (0-9), hyphens (" - "), underscores (" _ "), colons (" : "), and periods (" . "). An id attribute can not contain character references, such as escaped characters or ampersand-series.