This function is only found on the “Properties” tab of the “Objects and Animation” window and, when selected, only applies to the particular image/object selected. When enabled it makes that object transparent to selection so that an object below it can be selected, changed, moved (or in the case of a button with an operation) operated in Preview or EXE. Using the above example of the two Frames each with its own Button as a Child Object, with the Frames set to “Transparent to Selection” either Button can be selected and the Frames are ignored.