3.2.4. Attributes

In a start-tag, white space and attributes are allowed between the element name and the closing delimiter. An attribute specification typically consists of an attribute name, an equal sign, and a value, though some attribute specifications may be just a name token. White space is allowed around the equal sign.

The value of the attribute may be either:

• A string literal, delimited by single quotes or double quotes and not containing any occurrences of the delimiting character.
  NOTE - Some historical implementations consider any occurrence of the `>' character to signal the end of a tag. For compatibility with such implementations, when `>' appears in an attribute value, it should be represented with a numeric character reference. For example, `<IMG SRC="eq1.jpg" alt="a>b">' should be written `<IMG SRC="eq1.jpg" alt="a&#62;b">' or `<IMG SRC="eq1.jpg" alt="a&gt;b">'.

• A name token (a sequence of letters, digits, periods, or hyphens). Name tokens are not case sensitive.
  NOTE - Some historical implementations allow any character except space or `>' in a name token.

In this example, <img> is the element name, src is the attribute name, and `http://host/dir/file.gif' is the attribute value:

   <img src='http://host/dir/file.gif'>

A useful technique for computing an attribute value literal for a given string is to replace each quote and white space character by an entity reference or numeric character reference as follows:

                     ENTITY      NUMERIC
           CHARACTER REFERENCE   CHAR REF     CHARACTER DESCRIPTION
           --------- ----------  -----------  ---------------------
             HT                  	         Tab
             LF                  
        Line Feed
             CR                  
        Carriage Return
             SP                           Space
             "       "      "        Quotation mark
             &       &       &        Ampersand

For example:

   <IMG SRC="image.jpg" alt="First &quot;real&quot; example">

The `NAMELEN' parameter in the SGML declaration (9.5, "SGML Declaration for HTML") limits the length of an attribute value to 1024 characters.

Attributes such as ISMAP and COMPACT may be written using a minimized syntax (see 7.9.1.2 "Omitted Attribute Name" in [SGML]). The markup:

   <UL COMPACT="compact">

can be written using a minimized syntax:

   <UL COMPACT>

NOTE - Some historical implementations only understand the minimized syntax.