How to have something like _layout/CreatePage.aspx of our own

Recently I learnt rather many things thanks to a kind guy I met at MSDN forum, and one of which is this; how to have something like _layout/CreatePage.aspx of your own.

My motivation behind was the following.
I want to have some properties defined with sites. In the very much same sense that we have custom columns, or fields with content types.
I guess many has the same demand.

I thought that an application page could do, and this is going to be very similar to the CreatePage.aspx in the following sense.
- Invoked from the Site Actions menu, and
- Invoked under each site’s context and does what it is supposed to do for the site.
Therefore, the URL has to be http://host/(path to the site)/_layout/theAppPage.aspx.

To do so, you have the manifest.xml as below.
<Solution>
<TemplateFiles>
<TemplateFile Location="LAYOUTS\theAppPage.aspx" />
</TemplateFiles>
</Solution>

When deployed, this will create the aspx file into the C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\LAYOUTS folder, and it becomes available at a URL like above.

Cool!!