Decoration can be easily inserted in ABC notation using a set of characters.
Here’s a list of the most common decorations:
~ a roll, used mainly in Irish and Scottish music.
. *staccato* mark.
H *fermata* mark.
L accent or emphais.
M lowermordent
P uppermordent
Other decorations use the ! syntax, which is more explicit:
!trill!
!slide!
!arpeggio!
!mordent!
Here’s a simple sequence with some decoration thrown in:
X: 1
C D !trill!E2 | !mordent!D E F G | ~G3
For a full list of all available decorations, visit the official ABC notation reference website