下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
VAR_REPRESENTATION_SINGLE_LINE
(int)
var_representation() flag indicating that newlines should not be used for whitespace in variable representations.
VAR_REPRESENTATION_UNESCAPED
(int)
var_representation() flag indicating that strings should be encoded as single quoted strings with unescaped control characters.