[KCmilam]

Well I pushed another update. I've been using it to make a new options panel for an addon and realized that it had trouble opening prexisting addon xml files.

The cause of the bug was from the two different ways that Anchors, Insets, Sizes, and Values could be set.

Method 1:

<Anchors>
    <Anchor point="TOPLEFT">
        <Offset x="15" y="15" />
    </Anchor>
</Anchors>

Method 2:

<Anchors>
    <Anchor point="TOPLEFT">
        <Offset>
            <AbsDimension x="15" y="15" />
        </Offset>
    </Anchor>
</Anchors>

It should be able to read both methods now and display the layout of the addon after pasting the code in the xml tab and pressing Update Designer.