Why is the no evaluate selection button?

Why is there no "evaluate selection" button in the Editor menu that one always has to use the mouse to evaluate a selection, or the fn+shift+F7 keyboard shortcut?

Answer 1

[madhan ravi]

ctr+A %(->cmd in Mac)
ctr+enter 

[madhan ravi]

use section break in live editor to run a specific line

[Snoopy]

No, I mean for evaluating only a line in script file. I do not use live script. So suppose on a line I have x = 1. To execute this command I highlight it and then right click on it with my mouse and select evaluate selection. Why is there no button in the Editor bar that allows me to execute this line of command only?