After wondering for one or two month what's happening in a regular exression I used with a sayregexp command, I was assuming that regular expressions can never be fully understood by normal programmers. But now I found out that sayregexp has an undocumented feature: it's second parameter, the separator, uses a space character as default if it is omitted or set to an empty string of zero length. This means, that the three versions
sayregexp "a|b|c"
sayregexp "a|b|c" ""
sayregexp "a|b|c" " "
are all the same and will separate the matches with a space. Therefore it is not possible to directly concatenate the matches from a sayregexp without a separater between them.
The same observation had been made by @vkostas already in sept 2012 .
I don't want to suggest, that sayregexp should be changed, because that would break several existing scripts, including my own one. Instead it would be great, if @Florian could simply change the documentation and add a hint to the space character being used as default separator.