Invalid patterns evaluated as valid by is.regex()

[pieterjanvc]

Hi,

Let me start by saying I really like your package! Very useful :)

However, I found several patterns that throw an error in R (using stringr::str_detect()) although they are evaluated as valid RegEx by your is.regex() function. They are all related to the curly brace {. These patterns might be correct for other software, but in R they fail in all stringr functions and most of the base grep cases

Patterns that throw error:

• "{"
• "{}"
• "{1,2}" (this one is 'valid' with the base grep function, but returns incorrect results)
• "\d{1,2,3}"

Grtz, PJ