To improve readability of grammars, adopters can now use the new infix rule notation (#1836) to declare parsing rules used for infix operator parsing:

infix BinaryExpression on PrimaryExpression:
    '%' // <-- Highest precedence
    > '^'
    > '*' | '/'
    > '+' | '-';  // <-- Lowest precedence

PrimaryExpression infers Expression:
    '(' Expression ')' |
    {infer NumberLiteral} value=NUMBER;

Note that the previous tree-rewriting action based grammar is still (and always will be) supported.
In addition to better readability, the new notation also makes use of performance optimizations to speed up expression parsing by roughly 50% compared to the typical way of writing expressions.