Reserved Number Register Names (UNIX in a Nutshell: System V Edition)

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`	`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.)