Complex sentence: Type errors are sometimes considered to be syntax errors when they are detected at compile-time (which is usually the case when compiling strongly-typed languages), though it is common to classify type errors as semantic errors instead.
Split into simpler sentences: Type errors are sometimes considered to be syntax errors when they are detected at compile-time (which is usually the case when compiling strongly-typed languages). However, it is common to classify type errors as semantic errors instead.