Join characters - hyphen, apostrophe, comma
I have product names such as [5',5''-2H2]adenosine (where the '' is actually 2 apostrophes, not a double quote) and [1-13C]cellobiose and [1'-13C]cellobiose (where the apostrophe is the only difference between 2 different product names. The indexing was done with hyphen, apostrophe, comma and colon all set to join words and skip words less than 1 character. I am getting expected results when searching for [1-13C]cellobiose, but [1'-13C]cellobiose and [5',5''-2H2]adenosine are problems. I am not finding any apostrophes highlighted in my search results. It is the case that the apostrophe is always followed by either a comma, a hyphen, or another apostrophe. What happens when a join character joins a letter or number to another join character?
Two single-quote characters in a row will not be indexed, it will split the word. A "word join" character only allows it to join characters which are actual alphabet/numeric.
Having said that, I just had a brain wave and may have a solution for you.
You need to use Custom Meta fields.
A custom meta field of Text type is not subjected to the normal word indexing rules. It is indexed exactly as it is, so you can search for square brackets, commas, single quotes, etc.
You can make the field match either using "exact match" which means the user has to specify the full exact product name, or a "partial match" which means they can specify a portion of the name (e.g. adenosine or 2h2]ade)
Please see the Custom Meta Field page linked above for more details. You will need to specify meta tags on your product pages accordingly.