Help with understanding a macro

[Elvenbane-veknilash (Elvenbane)]

Pins are your friend

@Elvenbane-veknilash

Basic Help/Harm Macro

This will cast one spell when mousing over or targeting a friend and another when mousing over or targeting an enemy.

#showtooltip
/cast [mod:alt,@player] [@mouseover,help,nodead] HELP_SPELL; [@mouseover,harm,nodead] [harm] HARM_SPELL; HELP_SPELL

#showtooltip
/cast [mod:alt,@player] [@mouseover,help,nodead] Shadow Mend; [@mouseover,harm,nodead] [harm] Smite; Shadow Mend

@Udiza-earthen-ring

The first is that you have “alt” set as your self cast key. (That will override any uses of “alt” in macros.)

A common misconception. With regards to macros, the self cast key only initializes a variable SELFCAST that you can use in place of ctrl/shift/alt etc. It doesn’t automatically affect them at all.
https://wow.gamepedia.com/Macro_conditionals#Modifier_Variables