Literals that precede { in spark view engine.

Question

I was going through the spark view engine documentation and found a lot of literals showing up in code for which I couldn’t find any references. For e.g.

! , #, $ , !$ , ...

What are these for? What do the combinations mean? When do they come into use? Am I missing any more literals that precede or comes after {

Answer 1

Also ?{ for conditional output.

Answer 2

Found one:

The syntax $!{expression} can also be used if you want to ensure any null values and NullReferenceException that result from the expression will produce no output at all.