Feature summary (what you would like to be able to do and where):
A single source may be used many times in a Wikipedia article. It is good to provide page numbers and sometimes exact quotations, especially for claims that are contested. Doing so requires an entirely new ref tag and citation template. It would be better to have some mechanism that can reference an existing named ref tag but with added page and quote information.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Benefits (why should this be implemented?):
Ease of use would increase the use of page and quote data on citations increasing verifiability of information. Also, when a source is used for many different quotes, shared fields like access date and archive url may diverge unnecessarily, which would be avoided by having all quotes reference a single shared definition of the source.