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
A logical vector that is TRUE when the input contains valid
dates or times.
See Also
strptime for specifying formats, and the
lubridate package for automatic guessing of date formats (and other
date manipulation functions).