anchor.diff:  separate and logically-complete catalog, then create a master catalog
   using __catalog references__:
   
  +[source,xml]
   ---------------------------------------------------------------------------------------------------------------------------------
   <?xml version="1.0" encoding="UTF-8"?>
   <catalog xmlns="http://www.unidata.ucar.edu/namespaces/thredds/InvCatalog/v1.0" name="Top Catalog"
  -1    xmlns:xlink="http://www.w3.org/1999/xlink">
  -2  <dataset name="Realtime data from IDD" ID="IDD">
  -3    <catalogRef xlink:href="idd/models.xml" xlink:title="NCEP Model Data" name="" />
  -3    <catalogRef xlink:href="idd/radars.xml" xlink:title="NEXRAD Radar" name="" />
  -3    <catalogRef xlink:href="idd/obsData.xml" xlink:title="Station Data" name="" />
  -3    <catalogRef xlink:href="idd/satellite.xml" xlink:title="Satellite Data" name="" />
  -   </dataset>
  -
  -4  <catalogRef xlink:title="Far Away University catalog" xlink:href="http://www.farAway.edu/thredds/catalog.xml" />    <!-- 4 -->
  +    xmlns:xlink="http://www.w3.org/1999/xlink">  <!--1-->
  +  <dataset name="Realtime data from IDD" ID="IDD">  <!--2-->
  +    <catalogRef xlink:href="idd/models.xml" xlink:title="NCEP Model Data" name="" />  <!--3-->
  +    <catalogRef xlink:href="idd/radars.xml" xlink:title="NEXRAD Radar" name="" />  <!--3-->
  +    <catalogRef xlink:href="idd/obsData.xml" xlink:title="Station Data" name="" />  <!--3-->
  +    <catalogRef xlink:href="idd/satellite.xml" xlink:title="Satellite Data" name="" />  <!--3-->
  +  </dataset>
  +
  +  <catalogRef xlink:title="Far Away University catalog" xlink:href="http://www.farAway.edu/thredds/catalog.xml" />  <!--4-->
   </catalog>
   ---------------------------------------------------------------------------------------------------------------------------------
   
  -1.  We declare the *xlink namespace* in the catalog element.
  -2.  The _collection_ (or __container__) dataset logically contains the
  +<1> We declare the *xlink namespace* in the catalog element.
  +<2> The _collection_ (or __container__) dataset logically contains the
   `catalogRef`s, which are thought of as nested datasets whose contents
   are the contents of the external catalog.
  -3.  Here are several `catalogRef` elements, each with a link to an
  +<3> Here are several `catalogRef` elements, each with a link to an
   external catalog, using the `xlink:href` attribute. The `xlink:title` is
   used as the name of the dataset. We need a `name` attribute (in order to
   validate, for obscure reasons), but it is ignored. The `xlink:href`
   attributes are
   http://www.webreference.com/html/tutorial2/3.html[relative URLS] and are
   resolved against the catalog URL. For example, if the catalog URL is:
  -+
  -__________________________________________________
  -*http://thredds.ucar.edu/thredds/data/catalog.xml*
  -__________________________________________________
  -+
  +`http://thredds.ucar.edu/thredds/data/catalog.xml`
   then the resolved URL of the first `catalogRef` will be:
  -4.  `catalogRefs ` needn’t point to local catalogs only; this one points
  +`http://thredds.ucar.edu/thredds/data/idd/models.xml`.
  +<4> `catalogRef`s needn’t point to local catalogs only; this one points
   to a remote one at Far Away University.
  -5.  *The metadata elements with inherited=``true''* are NOT not copied
  +
  +The metadata elements with `inherited='true'` are NOT copied
   across catalogRefs. The *catalog* that a *catalogRef* refers to is
   stand-alone in that sense.
   
  
positive.code: services. Elements such as `summary`, `rights`, and `publisher` are
  needed in order to create valid entries for these services.
  
  ------------------------------------------------------------------------------------------------------------------------------------------------------------
  <dataset name="SAGE III Ozone Loss Experiment" ID="Sage III" harvest="true">
    <contributor role="data manager">John Smith</contributor>
  
negative.code: When you have many datasets to declare in each catalog, you can use
  nested datasets:
  
  [source,xml]
  -----------------------------------------------------------------------------------------------------
  <?xml version="1.0" ?>
  <catalog xmlns="http://www.unidata.ucar.edu/namespaces/thredds/InvCatalog/v1.0" >
    <service name="odap" serviceType="OpenDAP"  base="/thredds/dodsC/" />
  
    <dataset name="SAGE III Ozone Loss Experiment" ID="Sage III">  <!--1-->
      <dataset name="January Averages" serviceName="odap" urlPath="sage/avg/jan.nc" ID="jan.nc"/>  <!--2-->
      <dataset name="February Averages" serviceName="odap" urlPath="sage/avg/feb.nc" ID="feb.nc"/>  <!--2-->
      <dataset name="March Averages" serviceName="odap" urlPath="sage/avg/mar.nc" ID="mar.nc"/>  <!--2-->
    </dataset>  <!--3-->
  </catalog>
  -----------------------------------------------------------------------------------------------------
  
  <1> This declares a _*collection dataset*_ which acts as a container for
  the other datasets. Note that it ends in a `>` instead of `/>`, and does
  not have a `urlPath` attribute.
  <2> These are the datasets that directly point to data, called **_direct
  datasets_**.
  <3> This closes the collection dataset element on line 1.
  
  You can add any level of nesting you want, e.g.:
  
  [source,xml]
  ----------------------------------------------------------------------------------------------------------
  <?xml version="1.0" ?>
  <catalog name="Example" xmlns="http://www.unidata.ucar.edu/namespaces/thredds/InvCatalog/v1.0" >
  