How are action methods within Magento layout xml files intended to be used

Question

Examples

mylayoutfile.xml

 <layout>
        <default>
            <reference name="header">
                <block type="mynamespace_mymodule/view" name="mynamespace_mymodule" output="toHtml" template="mymodule/html/view.phtml">
                    <action method="setTest"><param1>myparam1</param1><param2>myparam2</param2></action>
                </block>
            </reference>
        </default>
    </layout>

app/code/local/Mynamespace/Mymodule/Block/View.php

    class Mynamespace_Mymodule_Block_View extends Mage_Core_Block_Template{
        public $test = "before any params";
            public function setTest($passedparam1,$passedparam2){
             $this->test = $passedparam1 ." ". $passedparam2;
            }

}

app/design/.../.../mymodule/html/view.phtml

<?php
echo "<pre>";
print_r($this->test);  //myparam1 myparam2
echo"</pre>";
die();

Explanation

mylayoutfile is compiled in an update through your modules config.xml

the block class prefix of mynamespace_module is also defined within your modules config.xml

mynamespace_module/view is set as the block type and instantiated and the output file of view.phtml is set

an action takes place that calls the parent node block's method setTest passing two parameters with the value of myparam1 and myparam2.

inside of the setTest function the class parameter "test" is set to equal "myparam1 myparam2"

the template file app/design/.../.../mymodule/html/view.phtml is loaded and we echo the value of $this->test ($this refers to the earlier instantiated block class Mynamespace_mymodule_Block_View)

QUESTIONS

1. What are some examples of use cases where this might be used?
2. Can you pass anything other than a string? (Object,Array)?
3. Do the automagical setters and getter methods work from inside a layout file?
4. Can logic be used (if,then,foreach,else,etc)?
5. Are there any scenarios where this method should not be used?
6. Is there anything else I might be missing related to block instantiation from within a layout file?
7. Is there anything else I might be missing related to actions from within a layout file?

Answer 1

1. Could be used for a multi-purpose template. Look at the use of setTitle in catalog.xml.

2. Anything can be passed. Arrays can be defined in layout XML:

   <action method="setFoo">
       <arbitrary>
           <key1>val1</key1>
           <key2>val1</key2>
       </arbitrary>
   </action>
   

   Also, argument nodes can execute a helper method, the return value of which will be passed in as the value:

   <action method="setFoo">
       <arbitrary helper="foo/bar" />
   </action>
   

   This would instantiate a helper & run a method: Mage::helper('foo')->bar(). The return value could therefore be anything you want. Additionally args can be passed to the helper in child nodes!

3. Blocks extend Varien_Object, so yes, though the setters are the only reasonable one to use.
4. There is no direct logic for this. The closest is the action's ifconfig attribute which will call Mage::getStoreConfigFlag() with the provided argument and process the action if the config value is true.
5. "[c]ould not be used" - no. "Won't matter" - yes.
6. There are lots of nuances (too many to go into here), but you've got a lot already. Alan Storm gets all nuance-y in his book, No Frills Magento Layout; nothing beats exploring the limits yourself though.