14.4 Reserved Number Register Names

The following number register names are used by the ms package. An italicized n means that the name contains a numeral (generally the interpolated value of another number register).

n T	AJ	AV	BC	BD	BE	BH	BI	BQ
BW	CW	EF	FC	FL	FM	FP	GA	GW
H1	H2	H3	H4	H5	HM	HT	I0	IF
IK	IM	IP	IR	IS	IT	IX	I n	J n
KG	KI	KM	L1	LE	LL	LT	MC	MF
MG	ML	MM	MN	NA	NC	ND	NQ	NS
NX	OJ	PD	PE	PF	PI	PN	PO	PQ
PS	PX	QI	QP	RO	SJ	ST	T.	TB
TC	TD	TK	TN	TQ	TV	TY	TZ	VS
WF	XX	YE	YY	ZN

When you're writing your own macros, the safest bet is to use mixed case letters for macro names. (Using uppercase letters could conflict with reserved ms names, and using lowercase letters could conflict with troff requests.)