When the TRANSCLUDE plugin, placed in Page A, fetches the wiki page B, the tag %%%text%%% on Page B is replaced by whatever is inside the TRANSCLUDE tag on Page A.
Furthermore, any other parameters (if they exist in Page B ) will be replaced by their values given in the Transclude plugin on Page A..

{TRANSCLUDE(page="pageName"  key="value" key="value" ...")}text{TRANSCLUDE}

For instance, say we have a todo box page with template like this:

{BOX(class="todo_box", float="right", title="__Todo__ on this page:")}
%%%text%%%{BOX}

It will render like this:

Now, let's use that template page to 'transclude' some todo items on a page:

{TRANSCLUDE(page="todoBox")}
* Bring out the garbage
* Feed the goldfish
{TRANSCLUDE}

All additional parameters will be replaced. For example %%%title%%% will be replaced with the parameter title in the plugin.

{TRANSCLUDE(page="todoBox" title="ToDo")}
* Bring out the garbage
* Feed the goldfish
{TRANSCLUDE}

• See more examples at http://www.ogre3d.org/tikiwiki/Help+-+Wiki+Plugins#a6df121fca50fcac3ee350341950ac9e3
• PluginInclude - similar plugin that includes content from other pages, but without changes