What is the '|' supposed to be an alternative of, the operand rule parenthesized expression?

A rule can have alternatives, e.g. rule_name: alt1 | alt2, and you can insert an action in the middle of a rule:

rule_name: alt1 {action} | alt2
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And, you can add whatever whitespace you want:

 rule_name: alt1
{action} 
 | alt2
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And you can add an action at the end of a rule:

 rule_name: alt1
{action} 
 | alt2 {action}
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