The expression creates a typing animation with a blinking cursor. Applies to the Source Text parameter of the text layer.

Speed = 10; // Speed typing
Blink = 2; // The speed of blinking cursor
CursorType = "|" // Type of the cursor. This is usually a vertical line "|" or the bottom dash "_"

F = Math.round(time*Blink % 1);
L = text.sourceText.length;
T = (time - thisLayer.inPoint)*Speed;
if(F ==1 | (T<L & T>0) ){Fl=CursorType;}else{Fl="";}
substr(0,T) + Fl