[meta] Expressions

[Hywan]

Address #11.

Specification

https://github.com/php/php-langspec/blob/master/spec/19-grammar.md#expressions

Progression

• Primary expressions,
• Postfix operators,
• Unary operators,
• Assignment operators:
  • Conditional operator,
    • instanceof operator,
    • Multiplicative operators,
    • Additive operators,
    • Bitwise shift operators,
    • Relational operators,
    • Equality operators,
    • Bitwise logical operators,
    • Logical operators (form 1),
    • Logical operators (form 2),
  • Coalesce operator,
• yield operator,
• Script inclusion operators,
• Constants expressions.