context

`Contextwriter' tags inside a context tag supplying the `id' attribute register themselves in the context. Other tags can refer to this id. See for example how the createrelation tag works. A special case of a another tag referring to this id is a tag of the same type. Normally with an attribute `referid' you could `repeat' the tag.

With the import tag you can explicitly put things from outside this context into this context, e.g. from the parameter list or from a parent context. It is also possible to put new strings in the context with the import tag.

There are several ways to refer to objects in the context.

When you are adding a new object then the used attribute is `id'.

The `id' of an `external' object like a request parameter is referred to as `externid' (only in the import tag).

If you are reusing the same object, for example you have put a node in the context, and are using it again then an attribute `referid' is used.

If some attribute wants to use the value of an object in the context, and it is an attribute which can refer to the context (which most attributes are), then you can use something like <context-id;>.<object-id>. The `context-id' is optional when you are in the same context, or sub-context. The value of a context variable can be written to the page with the `write' tag. The {}-parentheses are optional too.

And finally there are some attributes which can only refer. For example if some tag has to live as a child of another tag but you want it to refer not to its direct parent, then there should be an attribute with the name of the parent in which you can put the id of the parent which it has to refer to. For example the field tag has an attribute `node'. This kind of referring does not function per the ContextTag, and is only good for finding ancestor tags. Other tags, like the createrelation tag have attributes like `source' and `destination' attributes which also simply contain the node id's. Please find the examples.

In TCP there is a `tag' called `create', which is comparable to `context'.

On default a context has no id. The implicit `page' context also doesn't have. If a context has no id, there is no way of referring to variables of it if you are not in the context itself (or one of the sub-contexts).

• referid (since: MMBase-1.7)
  Pick up existing context.
  
• scope (since: MMBase-1.8)
  Pick up existing context.
  

  page
  request
  session
  application

• id

• context

Use a context inside another context (inside the default `context')
                and import parameters:
<mm:import id="hoi">greetings from amsterdam</mm:import>
<mm:import id="alias" externid="hoi" required ="true" />
<mm:context id="other_context">
  <mm:import externid="alias" />
  <mm:write referid="alias" /><br/>
  <mm:import id="hoi_again">greetings from hilversum</mm:import>
  <mm:write referid="hoi_again" />
</mm:context>