Table of contents

Appendices

5.4 Locator Attribute (

The attribute that supplies the data that allows an XLink application to find a remote resource (or resource fragment) is href. It Must, May, etc. be used on simple-type elements, and Must, May, etc. be used on locator-type elements.

The value of the href attribute Must, May, etc. be a URI reference as defined in [rfc2396], or must result in a URI reference after the escaping procedure described below is applied. The procedure is applied when passing the URI reference to a URI resolver.

Some characters are disallowed in URI references, even if they are allowed in XML; the disallowed characters include all non-ASCII characters, plus the excluded characters listed in Section 2.4 of [rfc2396], except for the number sign (#) and percent sign (%) and the square bracket characters re-allowed in [rfc2732]. Disallowed characters Must, May, etc. be escaped as follows:

1. Each disallowed character is converted to UTF-8 [rfc2279] as one or more bytes.

2. Any bytes corresponding to a disallowed character are escaped with the URI escaping mechanism (that is, converted to %HH, where HH is the hexadecimal notation of the byte value).

3. The original character is replaced by the resulting character sequence.

Because it is impractical for any application to check that a value is a URI reference, this specification follows the lead of [rfc2396] in this matter and imposes no such conformance testing requirement on XLink applications.

If the URI reference is relative, its absolute version Must, May, etc. be computed by the method of [xbase] before use.

For locators into XML resources, the format of the fragment identifier (if any) used within the URI reference is specified by the XPointer specification [xptr].

Following is a non-normative attribute-list declaration for href on an element intended to be simple-type.

<!ATTLIST simplelink
  xlink:href      CDATA           #REQUIRED
  ...>