---------

- Values of length 1 in a `tibble()` call are recycled prior to evaluating subsequent arguments, improving consistency with `mutate()` (#213).
- Recycling of values of length 1 in a `tibble()` call maintains their class (#284).
- `add_row()` now always preserves the column data types of the input data frame the same way as `rbind()` does (#296).
- `lst()` now again handles duplicate names, the value defined last is used in case of a clash.
- Adding columns to zero-row data frames now also works when mixing lengths 1 and 0 in the new columns (#167).
- The `validate` argument is now also supported in `as_tibble.tbl_df()`, with default to `FALSE` (#278).  It must be passed as named argument, as in `as_tibble(validate = TRUE)`.

Formatting
----------

- `format_v()` now always surrounds lists with `[]` brackets, even if their length is one. This affects `glimpse()` output for list columns (#106).
- Factor levels are escaped when printing (#277).
- Non-syntactic names are now also escaped in `glimpse()` (#280).
- `tibble()` gives a consistent error message in the case of duplicate column names (#291).