What is "H5" in Egyptian?

Question

There seems to be a general consensus that classical Egyptian had four "guttural" or "H-like" phonemes: h (building, /h/), ḥ (wick, /ħ/), ḫ (placenta?, /x/), and ẖ (animal's belly, /ç/). And the main works that I've seen exploring the historical phonology (e.g. Loprieno) haven't proposed any additional ones, to my knowledge.

However, the documentation for CLTK's MdC transliterator seems to mention a fifth:

Small and Capital H5: almost exclusively used for transliterating demotic script.

What is "H5"? Is this a different name for one of the "standard" phonemes, or a new discovery, or a fringe theory that isn't accepted by the mainstream? Or something else entirely?

Answer 1

"H5" or "fifth H" is generally transcribed either "h̭" or "ḫ₂", and represents what's very likely a phonemic split in later Egyptian.

At a certain point, Egyptian ḫ starts being written in two different ways in group-writing: when it's written with the sign ḫ on its own ("ḫ₁"), it corresponds to ϩ in Sahidic Coptic, and when it's written with ḫ followed by dual strokes ("ḫ₂"), it corresponds to Sahidic ϣ. For example, ḫr "road" is written with ḫ₁ in group-writing and leads to ϩⲓⲣ in Sahidic, while mḫr "box" is written with ḫ₂ in group-writing and leads to ⲙϣⲓⲣ in Sahidic.

In Demotic, the two are written with different glyphs (descending from the old hieratic ḫ uniliteral with and without dual strokes), so Demoticists have given them different transcriptions: ḫ versus h̭. And given the Sahidic evidence, they do seem to have been phonemically different. But the nature of the distinction isn't entirely clear—the dual strokes may have been used as a generic diacritic to indicate "something is different about this sound" in group-writing—and I haven't found any suggestion for how they might have been pronounced. So if someone finds such a suggestion, please do add another answer!