Light blue shadow on time line

Hi, I just started getting a light blue shado on the time line, and I am not sure why pr how it got there. It causes recording to stop at the end of the shadow. I am sure this is a feature rather than a bug, but I don’t get it, and can’t find mention in the manual. I am probably not looking for the right thing.

Thanks in advance. Dave

Windows 10 home
Audacity 2.2.2
I/O is Yamaha THR5 (works great)

Never mind. Definitely a feature.

Oops.

Was the “light blue shadow” a “selection” https://manual.audacityteam.org/man/audacity_selection.html#Selecting_regions_using_the_mouse

Not quite a selection, I think, but a handy tool. On this machine, with whatever settings I set, when a shorter section is toggled – selected – a recording from the start winds up stopping at the end of the shorter track. COuld be very handy. I have used Audacity for about several years and never rant into this. It confused me a bit. All good now. What a great tool it is.

Is this a baseline feature or what? It sounds very useful but I’ve never seen it before. How can I enable this?