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Lesson 7
The ID attribute is used to define a unique style for an element. A CSS rule such as
#wdg97 { font-size: larger }
may be applied in HTML through the ID attribute:
<P ID=wdg97>Welcome to the Web Design
Group!</P>
Each ID attribute must have a unique value over the document. The value must be an initial letter followed by letters, digits, or hyphens. The letters are restricted to A-Z and a-z.
Note that HTML 4.0 allows periods in ID attribute values, but CSS1 does not allow periods in ID selectors. Also note that CSS1 allows the Unicode characters 161-255 as well as escaped Unicode characters as a numeric code, but HTML 4.0 does not allow these characters in an ID attribute value.
The use of ID is appropriate when a style only needs to be applied once in any document. ID contrasts with the STYLE attribute in that the former allows medium-specific styles and can also be applied to multiple documents (though only once in each document).
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