Simple Pneumatic question

Good afternoon!

I was given my first assignment dealing with pneumatics and am sort of going through a crash course (taught by google) in the symbols and their meanings. One that I'm having some trouble finding (and not entirely sure if it's even valid) is attached.

This is an electronically activated (left side end piece) solenoid with a spring return (right side end piece), but I'm unsure of what the line extending from the end of the triangle on the right side piece towards the center means. Can anyone enlighten me?

Also, I've only been able to find different examples of entire valves, I haven't had any luck locating a document that breaks down the different symbols and shows all the variations and what they mean. If anyone knows of a resource like that and can share, that would be most appreciated!

Thanks in advance!

The reason I'm asking is that I have seen similar drawings without that line, so I just want to make sure I'm not going to plant a problem that someone else has to deal with down the line when they look at my prints

This is a good place to start: https://library.automationdirect.com/pneumatic-circuit-symbols-explained/

http://www.hydraulicspneumatics.com/other-technologies/chapter-4-iso-symbols

That's exactly what I needed Tom, thanks a ton!