[dokuwiki] Abbreviations or Explain plug-in?

I checked the abbreviations page and several postings about it to no avail, so 
hoping someone knows.

1.  Can abbreviations include non-alpha characters, e.g. can I use

$this_value$    This value is a special value

or would I have to use the explain plug-in to accomplish something like this?

2. Does anyone know the precedence order of abbreviations vs. explain, i.e. if 
"this", "value" and "$this_value$" are all defined which would win?

Thanks,

Bobby

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