LibGfx/JBIG2: Expand a comment

Userland/Libraries/LibGfx/ImageFormats/JBIG2Loader.cpp

@@ -795,7 +795,7 @@ static ErrorOr<void> decode_immediate_generic_region(JBIG2LoadingContext& contex
     u8 flags = data[0];
     bool uses_mmr = (flags & 1) != 0;
     u8 arithmetic_coding_template = (flags >> 1) & 3;               // "GBTEMPLATE"
-    bool typical_prediction_generic_decoding_on = (flags >> 3) & 1; // "TPGDON"
+    bool typical_prediction_generic_decoding_on = (flags >> 3) & 1; // "TPGDON"; "TPGD" is short for "Typical Prediction for Generic Direct coding"
     bool uses_extended_reference_template = (flags >> 4) & 1;       // "EXTTEMPLATE"
     if (flags & 0b1110'0000)
         return Error::from_string_literal("JBIG2ImageDecoderPlugin: Invalid flags");