Simple vs. Extended links

- for compatibility and simplicity

Two kinds of links:

extended - the general ones we have seen so far
simple - a restricted version of extended links: only for two-ended inline links (enough for HTML-style links)

Convenient shorthand notation for simple links:

  <xlink:simple href="..." show="..." actuate="..."/>

which is equivalent to:

  <xlink:extended>
    <xlink:resource role="local"/>
    <xlink:locator href="..." role="remote"/>
    <xlink:arc from="local" to="remote" show="..." actuate="..."/>
  </xlink:extended>

(show and actuate are optional.)