#Specification for PHP Facebook has dedicated all copyright to this specification to the public domain worldwide under the CC0 Public Domain Dedication located at . This specification is distributed without any warranty. (Initially written in 2014 by Facebook, Inc., July 2014) **Table of Contents** - [Introduction](01-introduction.md#introduction) - [Conformance](02-conformance.md#conformance) - [Terms and Definitions](03-terms-and-definitions.md#terms-and-definitions) - [Basic Concepts](04-basic-concepts.md#basic-concepts) - [Program Structure](04-basic-concepts.md#program-structure) - [Program Start-Up](04-basic-concepts.md#program-start-up) - [Program Termination](04-basic-concepts.md#program-termination) - [__halt_compiler](04-basic-concepts.md#__halt_compiler) - [The Memory Model](04-basic-concepts.md#the-memory-model) - [General](04-basic-concepts.md#general) - [Reclamation and Automatic Memory Management](04-basic-concepts.md#reclamation-and-automatic-memory-management) - [Assignment](04-basic-concepts.md#assignment) - [General](04-basic-concepts.md#general-1) - [Value Assignment of Scalar Types to a Local Variable](04-basic-concepts.md#value-assignment-of-scalar-types-to-a-local-variable) - [Value Assignment of Objects to a Local Variable](04-basic-concepts.md#value-assignment-of-objects-to-a-local-variable) - [ByRef Assignment for Scalar Types with Local Variables](04-basic-concepts.md#byref-assignment-for-scalar-types-with-local-variables) - [ByRef Assignment of Non-Scalar Types with Local Variables](04-basic-concepts.md#byref-assignment-of-non-scalar-types-with-local-variables) - [Value Assignment of Array Types to Local Variables](04-basic-concepts.md#value-assignment-of-array-types-to-local-variables) - [Deferred Array Copying](04-basic-concepts.md#deferred-array-copying) - [General Value Assignment](04-basic-concepts.md#general-value-assignment) - [General ByRef Assignment](04-basic-concepts.md#general-byref-assignment) - [Argument Passing](04-basic-concepts.md#argument-passing) - [Value Returning](04-basic-concepts.md#value-returning) - [Cloning objects](04-basic-concepts.md#cloning-objects) - [Scope](04-basic-concepts.md#scope) - [Storage Duration](04-basic-concepts.md#storage-duration) - [Types](05-types.md#types) - [General](05-types.md#general) - [Scalar Types](05-types.md#scalar-types) - [General](05-types.md#general-1) - [The Boolean Type](05-types.md#the-boolean-type) - [The Integer Type](05-types.md#the-integer-type) - [The Floating-Point Type](05-types.md#the-floating-point-type) - [The String Type](05-types.md#the-string-type) - [The Null Type](05-types.md#the-null-type) - [Composite Types](05-types.md#composite-types) - [The Array Type](05-types.md#the-array-type) - [Objects](05-types.md#objects) - [Resources](05-types.md#resources) - [Constants](06-constants.md#constants) - [General](06-constants.md#general) - [Context-Dependent Constants](06-constants.md#context-dependent-constants) - [Core Predefined Constants](06-constants.md#core-predefined-constants) - [User-Defined Constants](06-constants.md#user-defined-constants) - [Variables](07-variables.md#variables) - [General](07-variables.md#general) - [Kinds of Variables](07-variables.md#kinds-of-variables) - [Constants](07-variables.md#constants) - [Local Variables](07-variables.md#local-variables) - [Array Elements](07-variables.md#array-elements) - [Function Statics](07-variables.md#function-statics) - [Global Variables](07-variables.md#global-variables) - [Instance Properties](07-variables.md#instance-properties) - [Static Properties](07-variables.md#static-properties) - [Class and Interface Constants](07-variables.md#class-and-interface-constants) - [Predefined Variables](07-variables.md#predefined-variables) - [Conversions](08-conversions.md#conversions) - [General](08-conversions.md#general) - [Converting to Boolean Type](08-conversions.md#converting-to-boolean-type) - [Converting to Integer Type](08-conversions.md#converting-to-integer-type) - [Converting to Floating-Point Type](08-conversions.md#converting-to-floating-point-type) - [Converting to String Type](08-conversions.md#converting-to-string-type) - [Converting to Array Type](08-conversions.md#converting-to-array-type) - [Converting to Object Type](08-conversions.md#converting-to-object-type) - [Lexical Structure](09-lexical-structure.md#lexical-structure) - [Scripts](09-lexical-structure.md#scripts) - [Grammars](09-lexical-structure.md#grammars) - [Lexical analysis](09-lexical-structure.md#lexical-analysis) - [General](09-lexical-structure.md#general) - [Comments](09-lexical-structure.md#comments) - [White Space](09-lexical-structure.md#white-space) - [Tokens](09-lexical-structure.md#tokens) - [General](09-lexical-structure.md#general-1) - [Names](09-lexical-structure.md#names) - [Keywords](09-lexical-structure.md#keywords) - [Literals](09-lexical-structure.md#literals) - [General](09-lexical-structure.md#general-2) - [Integer Literals](09-lexical-structure.md#integer-literals) - [Floating-Point Literals](09-lexical-structure.md#floating-point-literals) - [String Literals](09-lexical-structure.md#string-literals) - [Single-Quoted String Literals](09-lexical-structure.md#single-quoted-string-literals) - [Double-Quoted String Literals](09-lexical-structure.md#double-quoted-string-literals) - [Heredoc String Literals](09-lexical-structure.md#heredoc-string-literals) - [Nowdoc String Literals](09-lexical-structure.md#nowdoc-string-literals) - [Operators and Punctuators](09-lexical-structure.md#operators-and-punctuators) - [Expressions](10-expressions.md#expressions) - [General](10-expressions.md#general) - [Primary Expressions](10-expressions.md#primary-expressions) - [General](10-expressions.md#general-1) - [Intrinsics](10-expressions.md#intrinsics) - [General](10-expressions.md#general-2) - [array](10-expressions.md#array) - [echo](10-expressions.md#echo) - [empty](10-expressions.md#empty) - [eval](10-expressions.md#eval) - [exit/die](10-expressions.md#exitdie) - [isset](10-expressions.md#isset) - [list](10-expressions.md#list) - [print](10-expressions.md#print) - [unset](10-expressions.md#unset) - [Anonymous Function Creation](10-expressions.md#anonymous-function-creation) - [Postfix Operators](10-expressions.md#postfix-operators) - [General](10-expressions.md#general-3) - [The `clone` Operator](10-expressions.md#the-clone-operator) - [The `new` Operator](10-expressions.md#the-new-operator) - [Array Creation Operator](10-expressions.md#array-creation-operator) - [Subscript Operator](10-expressions.md#subscript-operator) - [Function Call Operator](10-expressions.md#function-call-operator) - [Member-Selection Operator](10-expressions.md#member-selection-operator) - [Postfix Increment and Decrement Operators](10-expressions.md#postfix-increment-and-decrement-operators) - [Scope-Resolution Operator](10-expressions.md#scope-resolution-operator) - [Exponentiation Operator](10-expressions.md#exponentiation-operator) - [Unary Operators](10-expressions.md#unary-operators) - [General](10-expressions.md#general-4) - [Prefix Increment and Decrement Operators](10-expressions.md#prefix-increment-and-decrement-operators) - [Unary Arithmetic Operators](10-expressions.md#unary-arithmetic-operators) - [Error Control Operator](10-expressions.md#error-control-operator) - [Shell Command Operator](10-expressions.md#shell-command-operator) - [Cast Operator](10-expressions.md#cast-operator) - [Variable-Name Creation Operator](10-expressions.md#variable-name-creation-operator) - [`instanceof` Operator](10-expressions.md#instanceof-operator) - [Multiplicative Operators](10-expressions.md#multiplicative-operators) - [Additive Operators](10-expressions.md#additive-operators) - [Bitwise Shift Operators](10-expressions.md#bitwise-shift-operators) - [Relational Operators](10-expressions.md#relational-operators) - [Equality Operators](10-expressions.md#equality-operators) - [Bitwise AND Operator](10-expressions.md#bitwise-and-operator) - [Bitwise Exclusive OR Operator](10-expressions.md#bitwise-exclusive-or-operator) - [Bitwise Inclusive OR Operator](10-expressions.md#bitwise-inclusive-or-operator) - [Logical AND Operator (form 1)](10-expressions.md#logical-and-operator-form-1) - [Logical Inclusive OR Operator (form 1)](10-expressions.md#logical-inclusive-or-operator-form-1) - [Conditional Operator](10-expressions.md#conditional-operator) - [Coalesce Operator](10-expressions.md#coalesce-operator) - [Assignment Operators](10-expressions.md#assignment-operators) - [General](10-expressions.md#general-5) - [Simple Assignment](10-expressions.md#simple-assignment) - [byRef Assignment](10-expressions.md#byref-assignment) - [Compound Assignment](10-expressions.md#compound-assignment) - [Logical AND Operator (form 2)](10-expressions.md#logical-and-operator-form-2) - [Logical Exclusive OR Operator](10-expressions.md#logical-exclusive-or-operator) - [Logical Inclusive OR Operator (form 2)](10-expressions.md#logical-inclusive-or-operator-form-2) - [`yield` Operator](10-expressions.md#yield-operator) - [Script Inclusion Operators](10-expressions.md#script-inclusion-operators) - [General](10-expressions.md#general-6) - [The `include` Operator](10-expressions.md#the-include-operator) - [The `include_once` Operator](10-expressions.md#the-include_once-operator) - [The `require` Operator](10-expressions.md#the-require-operator) - [The `require_once` Operator](10-expressions.md#the-require_once-operator) - [Constant Expressions](10-expressions.md#constant-expressions) - [Statements](11-statements.md#statements) - [General](11-statements.md#general) - [Compound Statements](11-statements.md#compound-statements) - [Labeled Statements](11-statements.md#labeled-statements) - [Expression Statements](11-statements.md#expression-statements) - [Selection Statements](11-statements.md#selection-statements) - [General](11-statements.md#general-1) - [The `if` Statement](11-statements.md#the-if-statement) - [The `switch` Statement](11-statements.md#the-switch-statement) - [Iteration Statements](11-statements.md#iteration-statements) - [General](11-statements.md#general-2) - [The `while` Statement](11-statements.md#the-while-statement) - [The `do` Statement](11-statements.md#the-do-statement) - [The `for` Statement](11-statements.md#the-for-statement) - [The `foreach` Statement](11-statements.md#the-foreach-statement) - [Jump Statements](11-statements.md#jump-statements) - [General](11-statements.md#general-3) - [The `goto` Statement](11-statements.md#the-goto-statement) - [The `continue` Statement](11-statements.md#the-continue-statement) - [The `break` Statement](11-statements.md#the-break-statement) - [The `return` Statement](11-statements.md#the-return-statement) - [The `throw` Statement](11-statements.md#the-throw-statement) - [The `try` Statement](11-statements.md#the-try-statement) - [The `declare` Statement](11-statements.md#the-declare-statement) - [Arrays](12-arrays.md#arrays) - [General](12-arrays.md#general) - [Array Creation and Initialization](12-arrays.md#array-creation-and-initialization) - [Element Access and Insertion](12-arrays.md#element-access-and-insertion) - [Functions](13-functions.md#functions) - [General](13-functions.md#general) - [Function Calls](13-functions.md#function-calls) - [Function Definitions](13-functions.md#function-definitions) - [Return typing](13-functions.md#return-typing) - [Type check modes](13-functions.md#type-check-modes) - [Variable Functions](13-functions.md#variable-functions) - [Anonymous Functions](13-functions.md#anonymous-functions) - [Classes](14-classes.md#classes) - [General](14-classes.md#general) - [Class Declarations](14-classes.md#class-declarations) - [Class Members](14-classes.md#class-members) - [Dynamic Members](14-classes.md#dynamic-members) - [Constants](14-classes.md#constants) - [Properties](14-classes.md#properties) - [Methods](14-classes.md#methods) - [Constructors](14-classes.md#constructors) - [Destructors](14-classes.md#destructors) - [Inheritance](14-classes.md#inheritance) - [Methods with Special Semantics](14-classes.md#methods-with-special-semantics) - [General](14-classes.md#general-1) - [Method `__call`](14-classes.md#method-__call) - [Method `__callStatic`](14-classes.md#method-__callstatic) - [Method `__clone`](14-classes.md#method-__clone) - [Method `__debugInfo`](14-classes.md#method-__debuginfo) - [Method `__get`](14-classes.md#method-__get) - [Method `__invoke`](14-classes.md#method-__invoke) - [Method `__isset`](14-classes.md#method-__isset) - [Method `__set`](14-classes.md#method-__set) - [Method `__set_state`](14-classes.md#method-__set_state) - [Method `__sleep`](14-classes.md#method-__sleep) - [Method `__toString`](14-classes.md#method-__tostring) - [Method `__unset`](14-classes.md#method-__unset) - [Method `__wakeup`](14-classes.md#method-__wakeup) - [Serialization](14-classes.md#serialization) - [Predefined Classes](14-classes.md#predefined-classes) - [Class `Closure`](14-classes.md#class-closure) - [Class `Generator`](14-classes.md#class-generator) - [Class `__PHP_Incomplete_Class`](14-classes.md#class-__php_incomplete_class) - [Class `stdClass`](14-classes.md#class-stdclass) - [Predefined Error Classes](14-classes.md#predefined-error-classes) - [Class `Error`](14-classes.md#class-error) - [Class `ArithmeticError`](14-classes.md#class-arithmeticerror) - [Class `AssertionError`](14-classes.md#class-assertionerror) - [Class `DivisionByZeroError`](14-classes.md#class-divisionbyzeroerror) - [Class `ParseError`](14-classes.md#class-parseerror) - [Class `TypeError`](14-classes.md#class-typeerror) - [Interfaces](15-interfaces.md#interfaces) - [General](15-interfaces.md#general) - [Interface Declarations](15-interfaces.md#interface-declarations) - [Interface Members](15-interfaces.md#interface-members) - [Constants](15-interfaces.md#constants) - [Methods](15-interfaces.md#methods) - [Predefined Interfaces](15-interfaces.md#predefined-interfaces) - [Interface `ArrayAccess`](15-interfaces.md#interface-arrayaccess) - [Interface `Iterator`](15-interfaces.md#interface-iterator) - [Interface `IteratorAggregate`](15-interfaces.md#interface-iteratoraggregate) - [Interface `Throwable`](15-interfaces.md#interface-throwable) - [Interface `Traversable`](15-interfaces.md#interface-traversable) - [Interface `Serializable`](15-interfaces.md#interface--serializable) - [Traits](16-traits.md#traits) - [General](16-traits.md#general) - [Trait Declarations](16-traits.md#trait-declarations) - [Trait Uses](16-traits.md#trait-uses) - [Exception Handling](17-exception-handling.md#exception-handling) - [General](17-exception-handling.md#general) - [Class `Exception`](17-exception-handling.md#class-exception) - [Tracing Exceptions](17-exception-handling.md#tracing-exceptions) - [User-Defined Exception Classes](17-exception-handling.md#user-defined-exception-classes) - [Namespaces](18-namespaces.md#namespaces) - [General](18-namespaces.md#general) - [Defining Namespaces](18-namespaces.md#defining-namespaces) - [Namespace Use Declarations](18-namespaces.md#namespace-use-declarations) - [Name Lookup](18-namespaces.md#name-lookup) - [Grammar](19-grammar.md#grammar) - [General](19-grammar.md#general) - [Lexical Grammar](19-grammar.md#lexical-grammar) - [General](19-grammar.md#general-1) - [Comments](19-grammar.md#comments) - [White Space](19-grammar.md#white-space) - [Tokens](19-grammar.md#tokens) - [General](19-grammar.md#general-2) - [Names](19-grammar.md#names) - [Keywords](19-grammar.md#keywords) - [Literals](19-grammar.md#literals) - [General](19-grammar.md#general-3) - [Integer Literals](19-grammar.md#integer-literals) - [Floating-Point Literals](19-grammar.md#floating-point-literals) - [String Literals](19-grammar.md#string-literals) - [Operators and Punctuators](19-grammar.md#operators-and-punctuators) - [Syntactic Grammar](19-grammar.md#syntactic-grammar) - [Program Structure](19-grammar.md#program-structure) - [Variables](19-grammar.md#variables) - [Expressions](19-grammar.md#expressions) - [Primary Expressions](19-grammar.md#primary-expressions) - [Postfix Operators](19-grammar.md#postfix-operators) - [Unary Operators](19-grammar.md#unary-operators) - [instanceof Operator](19-grammar.md#instanceof-operator) - [Multiplicative Operators](19-grammar.md#multiplicative-operators) - [Additive Operators](19-grammar.md#additive-operators) - [Bitwise Shift Operators](19-grammar.md#bitwise-shift-operators) - [Relational Operators](19-grammar.md#relational-operators) - [Equality Operators](19-grammar.md#equality-operators) - [Bitwise Logical Operators](19-grammar.md#bitwise-logical-operators) - [Logical Operators (form 1)](19-grammar.md#logical-operators-form-1) - [Conditional Operator](19-grammar.md#conditional-operator) - [Coalesce Operator](19-grammar.md#coalesce-operator) - [Assignment Operators](19-grammar.md#assignment-operators) - [Logical Operators (form 2)](19-grammar.md#logical-operators-form-2) - [yield Operator](19-grammar.md#yield-operator) - [Script Inclusion Operators](19-grammar.md#script-inclusion-operators) - [Constant Expressions](19-grammar.md#constant-expressions) - [Statements](19-grammar.md#statements) - [General](19-grammar.md#general-4) - [Compound Statements](19-grammar.md#compound-statements) - [Labeled Statements](19-grammar.md#labeled-statements) - [Expression Statements](19-grammar.md#expression-statements) - [Iteration Statements](19-grammar.md#iteration-statements) - [Jump Statements](19-grammar.md#jump-statements) - [The try Statement](19-grammar.md#the-try-statement) - [The declare Statement](19-grammar.md#the-declare-statement) - [Functions](19-grammar.md#functions) - [Classes](19-grammar.md#classes) - [Interfaces](19-grammar.md#interfaces) - [Traits](19-grammar.md#traits) - [Namespaces](19-grammar.md#namespaces) - [Bibliography](20-bibliography.md#bibliography)