Comment by bluGill

Compilers often allow things in 11 that technically are not there until some later standard. Or sometimes things they have always allowed finally got standardized in a later version. Setting your standard to 11 if that is what you want to target it a good first step but don't depend on it - the real tests is all the compilers you care to support compile your code.

Even if you only target 11, there may be advantages to setting a newer version anyway. Sometimes the standard finally allows some optimization that would work, or disallows something that was always error prone anyway. I would recommend you set your standard to the latest the compiler supports and fix any bugs. Solve your we have to support older standards problem by having your CI system build with an older compiler (and also the newest one). C++ is very good at compatibility so this will rarely be a problem.