I suppose I would make a "link" some how, just like in an html page. What would the URL look like? What is the ActionScript command to open that other .mxml file? (Which may be a form or just another page)
Thanks in advance.
Either I didn't understand what is you requirement, or you have misunderstood some concepts about mxml files.
You can't make 'links' between mxml files. mxml files are compiled to bytecode that is executed by flash player.
Maybe what you need is to use another component in your mxml file. You have to add the component namespace to your app by using xmlins tag. Then you can use the component.
to open another .mxml file within your project? Like a sub window within your main app? You can do it as a popup;
var win:[MXML FILE NAME] = PopUpManager.createPopUp(this, [MXML FILE NAME], true) as [MXML FILE NAME];
or, if it's a completely different app you're trying to link to;
quite unsure about what exactly you want though...