[pmwiki-users] How does this Attach markup work?

[John W Morris]

%align=right%[[{$Name}?rb=0| Attach:gemini-redbt.gif"Close Rightbar"]]%%'''[[Right Bar]]'''

This is for the gemini and fixflow skin... but it is a markup question.
It seems to be setting a value for the variable "rb" on the named page but then there is the "|Attach:gemini-redbt.gif"
How is it determining where this file is? 
What is the syntax for "Attach:" ?
I have tried to search this and can't find anything on point.

Thanks
John Morris
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