# Trouble Grasping Square Brackets

**URL:** <https://forum.kirupa.com/t/trouble-grasping-square-brackets/235390>\
**Category:** flash\
**Created:** [August 10, 2007, 4:50pm UTC](https://forum.kirupa.com/t/trouble-grasping-square-brackets/235390 "2007-08-10T16:50:17Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![alanmace](https://avatars.discourse-cdn.com/v4/letter/a/3e96dc/32.png) [@alanmace](https://forum.kirupa.com/u/alanmace)\
**Post date:** [August 10, 2007, 4:50pm UTC](https://forum.kirupa.com/t/trouble-grasping-square-brackets/235390/1 "2007-08-10T16:50:17Z")

</div>

I’m reading a book on ActionScript and I’m in the section on controlling movie clips. I’m reading about the basic methods, and I’m starting to realize I still don’t fully understand the significance of square brackets. This is the example where I’m having trouble:

> baseClip.lineStyle(thickness:Number, [color:Number], [alpha:Number], [pixelHinting:Boolean], [noScale:String], [capsStyle:String], [jointStyle:String], [miterLimit:Number]) : Void  
> Obviously, this is the prototype form of the lineStyle() method. What I don’t get is why “thickness” is the only parameter without square brackets. I know that square brackets are used for retrieving data from an array or object, but either my book doesn’t cover why they’re used like this in a method, or I just completely blanked it out. Can someone help to clarify this for me?