Offline web content is readily done with an HTML5 Cache Manifest, as well described and demonstrated by Mark Pilgrim. Though the manifest file itself is simple, creating it can require some tedious work. This Coda Plugin attempts to address that. The guts of the plugin are a relatively simple perl script that gathers relative URL references from the open HTML file and generates a manifest. I wrote the perl script so that it can also be used as a stand-alone shell command too. From the manifest-gen script's "-h" option

Generates a default HTML5 'cache manifest' file from HTML input.

The manifest includes items referenced by HTML tags with attributes for href, longdesc, and src. The items are sorted with duplicates removed.

The manifest excludes items that specify a protocol scheme, i.e. non-relative URLs.

To install the plugin- just download, unzip, and double-click. Coda will open and install the plugin.

Coda plugin icon HTML5 Manifest Generator

To use, open an HTML file and use the Coda Plugins menu to select Manifest Generator. The command will open a new document with a sample manifest. Remember to save the file and add the manifest attribute to the <html> tag of the main HTML file. See Mark Pilgrim's excellent book for details.

Given sufficient interest I can also make the bare command/shell script of the command available for download. It works on a named file or you can pipe in standard input.