Arpeggios and glissandi

In Arpeggios and glissandi handbook page

"Short up/down slides can be created by editing the existing slide in / slide out lines. These have handles which allow you to set the length and angle of the slide."

"slide in / slide out lines" : may be "slide in/out lines"

"handles" (plural) : these slides symbols have only one handle, if we talk about the four at the bottom of the palette, else I misunderstand.
But maybe it's about : fall, doit, plop and scoop symbols.

Palette or score pic(s) would be appreciated, for me to clarify and maybe in the handbook.

Edit : "... of the symbol or turn it off altogether."
What does it mean ?

Thx