function validate( node ) {
		var requirePath;
		var pkg;
		if ( node.callee.name === 'require' ) {
			requirePath = node.arguments[ 0 ].value;
			if ( isString( requirePath ) ) {
				pkg = basename( requirePath );
				if ( !contains( requires, pkg ) ) {
					requires.push( pkg );
				}
			}
		}
	}
Checks for existence of require paths in the current program and registers them.

@private
@param {ASTNode} node - node to examine