Things to look up in the docs

[Don]

bearophile wrote:
> What are the parts of the D1/D2 languages that are both common enough in programs and not easy to remember, so you need to look them often in the docs (or in an example list, code snippets list, already written code, etc)? This list is partially subjective, but probably there are also some common trends.
> 
> For example the syntax of opApply is one of the things I have often to look up in the docs (while I never need the manual to remember how to write a generator in Python, that has very similar purposes).
> 
> Do you have other parts to add to this list?
> 
> Bye,
> bearophile

is() expressions.