"struts_action" param inside renderURL tag for liferay's MVCPortlet

[Jignesh Gohel]

<LIFERAY_PORTAL_SOURCE_HOME>/portal-web/docroot/WEB-INF/portlet-custom.xml

Following portlets has its class specified as "com.liferay.util.bridges.mvc.MVCPortlet"

Unit Converter, Loan Calculator, Password Generator, etc

In their view.jsp I can find the following:

<form action="<liferay-portlet:renderURL windowState="<%= LiferayWindowState.EXCLUSIVE.toString() %>"><portlet:param name="struts_action" value="/unit_converter/view" /></liferay-portlet:renderURL>" id="<portlet:namespace />fm" method="post" name="<portlet:namespace />fm">

<form action="<liferay-portlet:renderURL windowState="<%= LiferayWindowState.EXCLUSIVE.toString() %>"><portlet:param name="struts_action" value="/password_generator/view" /></liferay-portlet:renderURL>" id="<portlet:namespace />fm" method="post" name="<portlet:namespace />fm">

etc.

In the <liferay-portlet:renderURL> tag Portlet Params are passed like

<portlet:param name="struts_action" value="/unit_converter/view" />

I cannot find these actions in <LIFERAY_PORTAL_SOURCE_HOME>/portal-web/docroot/WEB-INF/struts-config.xml

And on debugging I see when the request reaches to com.liferay.util.bridges.mvc.MVCPortlet.doDispatch(RenderRequest, RenderResponse)
it uses the view configured in the parameter "view-jsp" i.e. again redirects to portlet's view.jsp

Ques. 1: Then what is the significance of passing the "struts_action" parameter in the render_url??

Ques. 2: Also in the same context each portlet has its resourceBundle configured as "com.liferay.portlet.StrutsResourceBundle".How does it work and where is the resource-bundle located as specified for the portlet?

Ques. 3: What is the decision criteria on when to use <liferay-portlet:renderURL> and <liferay-portlet:actionURL> tags? Do we have any documentation on th usage for
Liferay's tag libraries.If yes, then where can I find it.If no, then how to get familiar with the tag libraries usage fundamentals?