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The <o:methodParam> is a tag handler that can be used to pass a method expression as attribute into a Facelets tag. By default this is not possible, and the expression that's intended to be a method expression will be created and made available as a value expression.

This handler wraps a value expression that's actually a method expression by another value expression that returns a method expression that gets the value of first value expression, which as "side-effect" executes the original method expression. This somewhat over-the-top chain of wrapping is done so a method expression can be passed as attribute into a Facelet tag.