externalInfoUrl is always empty

Hello,

I'm new to FlexPMD. I have just generated my  firsts reports. I have just notice that the attribute externalInfoUrl is always empty.

<violation  beginline="22" endline="22" begincolumn="0" endcolumn="27"  rule="adobe.ac.pmd.rules.naming.TooShortVariable" ruleset="All Flex  Rules" package="utils.align" class="gridAlignSpaceNumber.as"  externalInfoUrl="" priority="5">This variable name is too short (3  characters minimum, but 1 actually). Detects when a field, local, or  parameter has a very short name</violation>

I  have 2 basics question :

- How externalInfoUrl can  be useful ?

- How I can fill it ?

Thanks !