In a Document Type Definition (DTD) an attributes type can be set to be NMTOKENS (name token list).

For a value to be a valid NMTOKENS the following must be true:-

  • It must conform to the EBNF for "Nmtokens". In simple terms it must contain one or more  NMTOKEN values separated by a single space.
[4]    NameStartChar       ::=       ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
[4a] NameChar ::= NameStartChar | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]
[7] Nmtoken ::= (NameChar)+
[8] Nmtokens ::= Nmtoken (#x20 Nmtoken)*

Declaring an IDREF Attribute in a DTD Copy Code
<!ELEMENT secureDocument EMPTY>
<!ATTLIST secureDocument authorizedUsers NMTOKENS #REQUIRED>
Sample XML Copy Code
<secureDocument authorizedUsers="James.Bond M Miss.MoneyPenny"/>


When an XML document is read in conjunction with a DTD the NMTOKENS value has the standard attribute whitespace normalization rules are applied plus an additional level of normalization.

3.3.3 Attribute-Value Normalization

Before the value of an attribute is passed to the application or checked for validity, the XML processor MUST normalize the attribute value by applying the algorithm below, or by using some other method such that the value passed to the application is the same as that produced by the algorithm.

  1. All line breaks MUST have been normalized on input to #xA as described in 2.11 End-of-Line Handling, so the rest of this algorithm operates on text normalized in this way.
  2. Begin with a normalized value consisting of the empty string.
  3. For each character, entity reference, or character reference in the unnormalized attribute value, beginning with the first and continuing to the last, do the following:
    • For a character reference, append the referenced character to the normalized value.
    • For an entity reference, recursively apply step 3 of this algorithm to the replacement text of the entity.
    • For a white space character (#x20, #xD, #xA, #x9), append a space character (#x20) to the normalized value.
    • For another character, append the character to the normalized value.

3.3.3 Attribute-Value Normalization

If the attribute type is not CDATA, then the XML processor MUST further process the normalized attribute value by discarding any leading and trailing space (#x20) characters, and by replacing sequences of space (#x20) characters by a single space (#x20) character.

See Also

Try Liquid XML Free and see how we can help you today Free Trial