Every weave is makes use of a pattern. The same web can look very different when woven with two different patterns; and a pattern can, in principle, be used with many different webs.

Like languages and notations, patterns are resources identified by their names. The default pattern is called HTML:

$ inweb weave pyramid.c.w
weaving web "Hilbert's Pyramid" (C program in MarkdownCode notation) as HTML

Note the as HTML at the end of that line. Whereas:

$ inweb weave pyramid.c.w -as GitHubPages
weaving web "Hilbert's Pyramid" (C program in MarkdownCode notation) as GitHubPages

That's to say, running the inweb weave command with the switch -as NAME tells Inweb to use the pattern called NAME.

Creating a whole new pattern is not as major an undertaking as it may first seem. Patterns can also be based on other patterns: for example, GitHubPages is based on HTML. It changes a few things, it adds a few things, but it doesn't need to sort out the many little details of making a web page. Anyone wanting to weave to web pages, but to pages which look different from Inweb's usual output, is almost certainly best advised to make a new pattern based on HTML (a generic sort of page-builder), and go from there.

Where patterns are declared

As mentioned above, a pattern is an Inweb resource, so it must have a declaration. But unlike (say) languages, this can't be declared inside of another declaration: it has to be in its own file, which contains nothing else. That's because a pattern is seldom just the declaration: it almost always comes with a suite of other files — holding HTML, Javascript code, CSS styles, TeX macros, images, or whatever else might be needed. So in practice

• a pattern called NAME should occupy a directory also called NAME, in which
• the actual declaration is in a text file called NAME.inweb.

As with other Inweb resources, patterns can only be used if Inweb can see them. Inweb has a handful of patterns built in, such as HTML and GitHubPages. Otherwise:

• -using DIRECTORY will tell Inweb it can use the pattern in that directory; or
• if a web is a multi-file web stored in a directory, and that directory has a subdirectory called Patterns, then Inweb will be able to see all patterns in that directory when weaving the web; or
• if a colony declaration includes patterns: DIRECTORY, then Inweb will be able to see all patterns in that directory when weaving any web from the colony.