Apologies for the title of the thread, I tried to be succinct.
Double-clicking the bottom-centre adjustment handle of a text frame shrinks the frame to the size of the visible text by adjusting the height while keeping the top of the frame where it is. This is a documented function.
Double-clicking the top-centre adjustment handle does similar but keeps the bottom of the frame where it is. As far as I can tell, this is an undocumented function.
That’s fine, but, as part of a discussion here https://forum.affinity.serif.com/index.php?/topic/100879-resize-text-frame-to-fit-copy-within/ I found that double-clicking the left-centre or right-centre adjustment handle of a text frame sometimes resizes the width of the frame. However, I couldn’t figure out what the resize criteria was. In other words, I don’t know how Publisher calculates the new frame width.
See my GIF in the linked thread for an example of each.
Does anyone know how the new frame width is calculated?