gistfile1.js

var fez = require("../../src/main.js"),
    less = require("fez-less"),
    clean = require("fez-clean-css"),
    concat = require("fez-concat");


// Example starting files:
// css/reset.css; main.less; mobile.less

exports.build = function(spec) {
  spec.with("dist/*.min.css").all(function(files) {
    spec.rule(files.array(), "dist.min.css", concat());
  });

  spec.with("css/*.css").each(function(file) {
    spec.rule(file.name(), fez.mapFile("dist/%f.min.css"), clean());
  });

  spec.with("*.less").each(function(file) {
    spec.rule(file.name(), fez.mapFile("css/%f.css"), less());
  });
};

exports.default = exports.build;

fez(module);

So what happens here is

at the first iteration, fez applies all the globs to the real filesystem and gets 3 files, as well as the operations they need to generate.