Issue #29004: Document binascii.crc_hqx() implements CRC-CCITT
diff --git a/Doc/library/binascii.rst b/Doc/library/binascii.rst
index 5eb7c4b..38f616a 100644
--- a/Doc/library/binascii.rst
+++ b/Doc/library/binascii.rst
@@ -101,8 +101,10 @@
.. function:: crc_hqx(data, crc)
- Compute the binhex4 crc value of *data*, starting with an initial *crc* and
- returning the result.
+ Compute a 16-bit CRC value of *data*, starting with an initial *crc* and
+ returning the result. This uses the CRC-CCITT polynomial
+ *x*:sup:`16` + *x*:sup:`12` + *x*:sup:`5` + 1, often represented as
+ 0x1021. This CRC is used in the binhex4 format.
.. function:: crc32(data[, crc])