PHP constant definition define vs. const

Briefly summarize the differences between two constants in PHP that define keywords:

1, define is a function, const is the language structure, PHP compile-time const fast.
2, define can only be used outside the class, Const class within the class can be.
3. Constants defined by define are global, and const-defined constants are limited by namespaces.
4, define can be used in conditional statements, Const cannot.
5, define can be used as the name of the expression, const only the ordinary constant name.
6, const can only accept static scalar, and define can use any expression.
7, const-defined constants are case-sensitive, and define can specify case sensitivity by the third argument (true for case insensitivity).

PHP constant definition define vs. const