I have 2 buttons next to a textbox and another textbox after the 2 buttons. The tabindex for the first textbox is 1000, the first button is 1001 and the second button is 10
For those like me also looking how to enable this in browserstack: simply click the word "Safari" in the top left button of the screen, then you can select Preferences > Advanced > Press tab (as mentioned in https://stackoverflow.com/a/1914496/11339541)