The problems I have are often related to how to use a certain library or a certain function in a programming language I don't know that well, in which case I often try to search for similar code on github to see examples, or look at the library code.

For stuff like "are there optional parameters in .len()?", I always keep a tab or two on both the documentation of the language and the library I'm using at the moment. I really like how some languages come with specific tools for documentation (ri in Ruby, the `doc` function in Clojure) and I try to use them as much as I can when available.