I've been going through the book "The Definitive Guide to Rails" (Rocher/Brown) and in Chapter 04, this mysterious thing called a "layout" just appeared with no explanation. (And there's no "layout" in the index. As far as I know, it's never explained.)
How does the system know to "inherit" the pages from layout/main.gsp? There's nothing about "layouts" in the index, and it seems to have just appeared.
On their sample app, a simple store site, the URL mappings for the / homepage say
"/"(controller:"store")
and store controller's empty "index" closure
package com.g2one.gtunes
class StoreController {
def index = {
}
}
simply tells it to render store/index.gsp
The store/index.gsp just has a few lines of HTML; no layout gets included with any directive
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
<meta name="layout" content="main">
<title>gTunes Store</title>
<g:javascript library="prototype"></g:javascript>
</head>
<body id="body">
<h1>Your online music store and storage service!</h1>
<p>Manage your own library, browse music and purchase new tracks as they become available</p>
</body>
</html>
When I run the sample the page shown for "/" isn't just this simple HTML, it's the contents of "layouts/main.gsp" with this information magically inserted inside it.
I don't see how the information in layout/main.gsp gets applied to the page, how the elements get mixed together. I've been following through the book page by page and this functionality just "appeared' with no explanation.