hl-line-sticky-flag

hl-line-sticky-flag is a variable defined in `hl-line.el'.
Its value is

t

Documentation:
Non-nil means the HL-Line mode highlight appears in all windows.
Otherwise Hl-Line mode will highlight only in the selected
window. Setting this variable takes effect the next time you use
the command `hl-line-mode' to turn Hl-Line mode on.

This variable has no effect in Global Highlight Line mode.
For that, use `global-hl-line-sticky-flag'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.