Using a workspace structure
If by “workspace structure” you mean you have defined a Workspace in an active Project Panel, then you can use the Project Panel > RightClick > Find in Projects… action (equivalent to using Ctrl+F to bring up the Find dialog, and changing to the Find in Projects tab). Then search for FIND WHAT = \A(?s:.) to find the first character in a file, and set any FILTERS as necessary to only find the right kinds of files. It would then search in all the files in whichever Project Panel checkbox(es) are checkmarked.
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Other than that, just searching the workspace.xml is a reasonable workaround.