Intro And Tab Notation Question

Greetings all,

First an introduction. I'm close to being an intermediate level guitar player, with the goal of becoming a guitarist and musician. I study a lot of theory as well as technique and I'm interested in blues, funk, country, reggae and many other styles of music. I have a 2010 Gibson LP Worn Brown, a 1996 MIM Strat which is heavily modifed (nothing original except wood and frets), and a 1957 Fender Duo-Sonic. In addition I have a Takamine acoustic/electric but the majority of my focus right now is on electric. I have two amps, a Marshall Lead 20 from the '80s and a Blackstar HT5R combo. Lots of other related stuff but truly, I just wanted to introduce myself as a fellow student. I've got a 3 year old boy, who loves music as well, and a guitar widow for a wife, though she tries to be very understanding. Me, I'm an old hippie that looks like I should play in a band (ZZ Top or Lynyrd Skynryd people tell me), and that's one of my goals. I practice often. Very often and as I've retired on disability I have the time to do this. Anyway, enough about me and on to my question

I've read the tab legend but don't see mention of E, S and Q above the tab and below the chords. My guess is it's some kind of shorthand for timing as some of the letters are dotted but I need clarification. In particular I'm studying the lesson titled Soul/ R & B by Stephane Lucarelli.

Any help of what the E, S and Q mean would be much appreciated.

Glad to be here, and hope to contribute to others in some way or another.

Kind Regards,
Black6host