simplify the Escape() function a little further
identify the captured window only once

Get a handle for it first, and then use that handle.  Don't get two
potentially different handles and be working with information from
two potentially different sources.
store window control data in a global variable

Previously this was local data because it wasn't needed after building
the TreeView.  Soon, this data will be needed for building clipboard
text after a GUI event occurs.
give Capture button handle variable a better name

Soon there will be multiple buttons on the GUI.
simplify ClassNameNN TreeView item creation

Greatly.  I'm really not sure why it wasn't done this way in the first
place, as the StringSplit() function appears to have been available
since the first release of AutoIt v3.
give "in capture mode" variable a better name

There's a difference between when the GUI is in capture mode and when
the script is actually capturing data (and populating the GUI with that
data).  Soon, the script will need to make that distinction.
move GUI state management into its own function

When the GUI has more controls, the logic for deciding what's enabled
etc. will be centralised here.
disable Capture button while capturing data
disable the TreeView while in capture mode

Forces the user to exit capture mode if they wish to further browse the
TreeView's content.
simplify capture mode toggling code
provide hint for user's next required action
make control placement variables more semantic
add "Copy Item" button

Copies the text of the currently selected TreeView item to the
clipboard.  Thanks to AutoIt Forums user "big_daddy" for providing an
initial implementation:

http://www.autoitscript.com/forum/topic/22490-find-classes-by-text-v11/#entry158637
add "Copy All" button

Copies all of the TreeView's content to the clipboard.  Thanks again to
AutoIt Forums user "big_daddy" for providing an initial implementation:

http://www.autoitscript.com/forum/topic/22490-find-classes-by-text-v11/#entry158637