What is a language construct? How is (theoretically) implemented in C?

Question

I am familiar with how PHP functions map to functions in C in C code under PHP. I know that C means function and what MACRO () means.
I don’t understand what a language construct like echo is in PHP.

Answer 1

"Language constructs" are operations that are supported by special functions in the language. In PHP, basically everything that is not a variable or function is a language construct, as indicated on the keyword list page.

As a PHP user, you have no way to implement new language constructs. They exist only at the parser level. It seems your goals are similar to yours and the answer will be the same.