See https://github.com/TeX-Live/luatex/blob/f52b099f3e01d53dc03b315e1909245c3d5418d3/source/texk/web2c/luatexdir/luafontloader/src/luafflib.c#L2772-L2774

diff --git a/manual/luatex-fontloader.tex b/manual/luatex-fontloader.tex
index 1e12b61f1..055228bcd 100644
--- a/manual/luatex-fontloader.tex
+++ b/manual/luatex-fontloader.tex
@@ -306,7 +306,7 @@ the documentation are not yet finished):
  \starttabulate[|l|l|p|]
  \DB key                                 \BC type     \NC explanation \NC \NR
  \TB
-\NC \type{table_version}                \NC number   \NC indicates the metrics version (currently~0.3)\NC \NR
+\NC \type{table_version}                \NC string   \NC indicates the metrics version (currently~0.3)\NC \NR
  \NC \type{fontname}                     \NC string   \NC \POSTSCRIPT\ font name\NC \NR
  \NC \type{fullname}                     \NC string   \NC official (human-oriented) font name\NC \NR
  \NC \type{familyname}                   \NC string   \NC family name\NC \NR