A logical value. If FALSE, NA values
cause an error; otherwise they do not. Like na.rm in many
stats package functions, except that the position of the failing
values does not change.
severity
How severe should the consequences of the assertion be?
Either "stop", "warning", "message", or "none".
.xname
Not intended to be used directly.
Value
is_single_character returns TRUE when the input is a
single character (as determined by nchar; this excludes NA).
The assert_* functions return nothing but throw an error if the
corresponding is_* function returns FALSE.