It's just like unix directory paths. If it starts with "/", it's an absolute path (i.e. relative to the root). 
//atom:entry

[download]

is short for 

/descendant::atom:entry

[download]

which requests all descendants of "/" (root) which are "atom:entry" elements. You want all descendants of the current node, so you want one of the following: 

descendant::atom:entry      # No leading "/" = rel to current node
./descendant::atom:entry    # "." = current node
.//atom:entry               # Shortcut

[download]

In reply to Re: xpath problem with XML::XPath and LibXML by ikegami
in thread xpath problem with XML::XPath and LibXML by woosley

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