Creating webpages with the MMBase Tag Library

The answer is that on default it will use the direct parent, so in this case the 'relatednodes' node provider.

If however this is not what you want then you need to know the following. Every tag, so also every node provider, can have an 'id' attribute, and every node referrer tag can have the 'node' attribute. So perhaps you understand already, but the example will make it clear if not:

<mm:node id="abc" number="123">
  <mm:relatednodes type="urls">
      <mm:field node="abc" name="title" />
  </mm:relatednodes>
</mm:node>        

This mechanisms work for every provider/referrer pair. So cloud-referrers have a 'cloud' attribute, node-referrers have a 'node' attribute and field-referrers have a 'field' attribute.

But the write-tag is also a writer referrer tag. Of course, when the write-tag works as a writer-referrer tag, it simply takes the content of the 'writer' tag it refers to and uses that as its own content.

<mm:field name="title">
  <mm:write />
</mm:field>

Most tags do have a referid attribute, to facilitate this.

It can happen you want to use the value of some writer in the attribute of another tag. This would be the natural thing to do:

<mm:field id="type" name="type" />
<mm:listnodes type="<mm:write referid="type" />"> <!-- THIS IS NOT POSSIBLE -->
   ..
</mm:listnodes>

To solve this, we came up with the dollar-sign notation:

<mm:field id="type" name="type" />
<mm:listnodes type="$type"> 
   ..
</mm:listnodes>

It is also more or less the notation of EL, though there it is obligated to use also curly brackets (they used to be optional in MMBase Taglib).

This will write out the field 'title' six times:

<mm:field id="title" name="title" /> simple
<mm:write referid="title" />         referid
<mm:write value="$title" />          MMBase dollar sign notation
<mm:write value="${title}" />        MMBase dollar sign notation with curly brackets, or EL if available
<mm:write value="$[title]" />        MMBase dollar sign notation with square brackets (introduced to provide way to avoid collisions with EL)
${title}

Dollar-sign variables can be used in nearly all attributes. It can also be combined with other text:

<mm:field id="title" name="title" />
<mm:listnodes type="news" constraints="title LIKE '$title'"> 
   ..
</mm:listnodes>

<mm:field id="firstname" name="firstname" />
<mm:field id="lastname" name="lastname" />
<mm:listnodes type="news" constraints="title LIKE '${firstname}${lastname}'"> 
   ..
</mm:listnodes>

Also other objects in the context can be used with a dollar-sign variable, and usually something sensible happens then. For example the dollar-sign value of a node is its number. You can use this for example to create an url:

<mm:listnodes id="article" type="news">
    <a href="<mm:url page="newsitem.jsp?article=$article" />"><mm:field name="title" /></a>
</mm:listnodes>

Very often you will be content with a taglib variable with the same name, so the 'id' attribute is optional if you use the externid attribute:

<mm:import externid="greeting" from="parameters"/>

These are the basics of the import tag. We refer to the taglib reference documentation for a full description.

Something similar goes for 'nodes' which are the core of any MMBase code, and also in taglib you may often want to refer to the 'current' node. As you can refer to the current writer with a nude <mm:write /> tag, so you can refer to the current node with a nude <node /> tag. The associated $-variable is $_node.

In that way you e.g. also easily use field values in attributes.

<mm:listnodes type="news">  
  <div class="${_node.className}">
  </mm:div>
</mm:listnodes>

<mm:listnodes type="news">  
  <div title="${mm:escape('text/html/attribute', _node.title)}">
  </mm:div>
</mm:listnodes>