Less.js: Parser documentation?

The server side usage references a configuration that can be passed into the Parser:
http://lesscss.org/#usage
var parser = new(less.Parser)({
paths: ['.', './lib'], // Specify search paths for @import directives
filename: 'style.less' // Specify a filename, for better error messages
});

parser.parse('.class { width: (1 + 1) }', function (e, tree) {
tree.toCSS({ compress: true }); // Minify CSS output
});

Is their any documentation as to what that configuration can contain? Can it contain variables?