The SYNTAX fields in the command descriptions contain references to items
explained here:

ARG        argument         Single numerical value
RANGE      range            Two numerical values
LIST       list             Three numerical value
VALUE      numerical value  EXPRESSION

CONDITION  test             One of EQ, NE, LE, LT, GE, GT

STRING     text             May include any characters but current
                            separating character
ANY        text             May include any characters but double-ESC
FILE       filename         A STRING without ESC or RETURN
TERM       terminator       An ESC or RETURN
/          separator        The / is commonly used, but arbitrary
REG        register name    The one-character name for a register
REGLIST    register list    Any number of concatenated register names