InputRegexp may be used in place of InputLiteral to recognize line ter
+minators based on a regular expression.
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I believe this is the important point.

I think what you trying to achieve is beyond what POE::Filter::Line can do by itself. Maybe POE::Filter::Block would be a better?

The other option is to use POE::Filter::Line with a custom filter in a stackable filter POE::Filter::Stackable.