[vte] emulation: Some more docs

[Christian Persch <chpe src gnome org>]

commit 970ea4ec4db308cf498b22c9ac94ae29559d7a11
Author: Christian Persch <chpe src gnome org>
Date:   Sat Aug 14 21:45:46 2021 +0200

    emulation: Some more docs

 src/vteseq.cc | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/vteseq.cc b/src/vteseq.cc
index 531bcfec..d92d13ad 100644
--- a/src/vteseq.cc
+++ b/src/vteseq.cc
@@ -6264,6 +6264,10 @@ Terminal::IRR(vte::parser::Sequence const& seq)
         /*
          * IRR - identify-revised-registration
          *
+         * Note that the IRR comes _before_ the GnDm/GnDMm/CnD, see e.g.
+         * IR#124 whose C1 designation sequence is ESC 2/6 4/0 ESC 2/2 4/2,
+         * i.e. IRR '@', C1D 'B'.
+         *
          * References: ECMA-35 § 14.5
          *
          * Probably not worth implementing.