Suggestion
===
Allow start a new GREP search session with a new window.
A use case
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Assuming I'm in the middle of reviewing/checking/changing references to a specific function where the amount is not small, and now I need to do another global search for another identifier.
A current workaround
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Combine the using of the IDE's Find In Files menu.
PS, Sorry, I came up with this workaround after finishing writing the above, but FWIW, I still post this suggestion.