  ++ L I N E   N O .   A R G U M E N T ++
 Many commands take one of these - some take two. They are always mandatory
parameters (sometimes called arguments) and must be numeric with a value
greater than zero but not greater than the number of lines in the file (except
that C-COPY and R-REPOSITION can accept 'EOF' - see their help for more
details). Exception:- the Y-CHANGEALL command has an optional line # parameter
with the default being 1 (start at beginning of file).
 The T<tab-id> format as described for # of lines parameters (H #L for details)
is also available for line numbers, but again will be mainly useful for macro
writing. For line numbers there is the additional restriction that tabs that
have or could have been set by the T-TABSET command cannot be used e.g. if you
have tabs set at 7 & 36 then tab-id's 1 & 2 are not available for line numbers.

Relative numbering
 An offset from the current file position ('H FP' for clarification) can be
specified by by giving a signed number. E.g. "-1" => previous line (line just
modified, for instance). Unary plus or minus is treated as zero offset, i.e.
operate on current line. Once the offset is added to the current file position,
the same range checks (0<result<=#lines) is applied.

Examples
 MOD -1     /* Modify the previous line
 GO +23     /* Move 23 lines on down file (to do another V-VIEW perhaps).
