Add missing pseudo-keywords & special vars, update operator precedence

[ifcologne]

Preview:

• https://deploy-preview-165--zealous-morse-14392b.netlify.com/docs/3.5/aql/fundamentals-syntax.html#keywords
• https://deploy-preview-165--zealous-morse-14392b.netlify.com/docs/3.5/aql/operators.html

[ifcologne]

Btw. should we add the pseudo-variables OLD and NEW to the variables section as well?

[Simran-B]

I went through the list of (key-)words using a simple query FOR doc IN coll RETURN doc.<word> and wrote down which are keywords (and their subtype), which are keyword-like and which are not keywords, see PrismJS/prism#2047

[Simran-B]

Note to self: do the special vars OLD and NEW shadow equally named variables? What is the scope? Can they be escaped to access the original variable value, or will that be equivalent to a quoted string literal?

[Simran-B]

An unquoted string literal is called an identifier:
https://github.com/arangodb/arangodb/blob/devel/arangod/Aql/grammar.y#L247

Missed non-reserved words:

• KEEP in COLLECT ... INTO ... KEEP
• COUNT in COLLECT ... WITH COUNT INTO
• PRUNE (FOR operation, before OPTIONS etc.)
• CURRENT in inline expressions, e.g. arr[* RETURN CURRENT * 2] (this is actually a special var)

Possible optimizations for PrismJS:

• OPTIONS must be followed by object ({ … }), however, there could be comments in between