[jQuery] Question on : syntax

[expresso]

I have yet another syntax question.

I know that : can be used for specifying things like filters, but what
does it do in this case:

    $jc.fn.extend({

        setup: function() {
            this.first     = null;
            this.last      = null;
            this.prevFirst = null;
            this.prevLast  = null;
            this.animating = false;
            this.timer     = null;
            this.tail      = null;
            this.inTail    = false;

            if (this.locked)
                return;

            this.list.css(this.lt, this.pos(this.options.offset) +
'px');
            ...rest of code here
        },

so what is the syntax setup:    an attribute?