Well, the real issue then seems to be that .roman2numeric uses an invalid
regular expression:
>> grepl("^M{,3}D?C{,4}L?X{,4}V?I{,4}$", cc)
> [1] TRUE TRUE TRUE TRUE TRUE
or
>> grepl("^I{,2}$", c("II", "III", "IIII"))
> [1] TRUE TRUE FALSE
Both the TRE and the PCRE specification only allow repetition quantifiers of
the form
{a}
{a,b}
{a,}
https://laurikari.net/tre/documentation/regex-syntax/
https://www.pcre.org/original/doc/html/pcrepattern.html#SEC17
{,2} and {,4} are thus invalid and seem to result in undefined behaviour (which
PCRE and TRE fill in different ways, but consistently not what was intended).
> > grepl("^I{,2}$", c("II", "III", "IIII"))
> [1] TRUE TRUE FALSE
> > grepl("^I{,2}$", c("II", "III", "IIII"), perl=TRUE)
> [1] FALSE FALSE FALSE
Fix thus is easy: {,4} => {0,4}
Best,
Stephanie
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