Questions on Nim's grammar

[lyhokia]

1\. I notice that Nim's grammar has this rule: 
    
    
    castExpr = 'cast' ('[' optInd typeDesc optPar ']' '(' optInd expr optPar 
')') /
    
    
    Run

An ordered choice followed by nothing, can anyone tell me what this means?

2\. What does `\` mean in nim's grammar? I don't find any interpretations. Does 
this mean the operator except(i.e. `A - B` matches iff A matches but B fails) 
in EBNF?

Thanks a lot!