While looking through the SolrMarc wiki, it seems to me that we don’t have a page documenting the operators that are legal in the index specification file. I’m aware, at the very least, of “=” and “+=” and “?=”. I imagine there may be others. I have a feeling that this may have even been discussed on this list before, but it’s hard to search for these operators since search engines do a poor job with random symbols. 😊 I also tried to figure out where they are defined in the code, but had no luck there either; usually I can dig things up in the .lex file, but I didn’t see them at that level.
Anyway, I bring this up for two reasons: