When a string is literal (contains no variable substitutions), the apostrophe or "single quote" should always be used to demarcate the string:

$a = 'Example String';

When a literal string itself contains apostrophes, it is permitted to demarcate the string with quotation marks or "double quotes". This is especially useful for SQL statements:

$sql = "SELECT `id`, `name` from `people` "
     . "WHERE `name`='Fred' OR `name`='Susan'";

This syntax is preferred over escaping apostrophes as it is much easier to read.

Variable substitution is permitted using either of these forms:

$greeting = "Hello $name, welcome back!";

$greeting = "Hello {$name}, welcome back!";

For consistency, this form is not permitted:

$greeting = "Hello ${name}, welcome back!";

Strings must be concatenated using the "." operator. A space must always be added before and after the "." operator to improve readability:

$company = 'Zend' . ' ' . 'Technologies';

When concatenating strings with the "." operator, it is encouraged to break the statement into multiple lines to improve readability. In these cases, each successive line should be padded with white space such that the "."; operator is aligned under the "=" operator:

$sql = "SELECT `id`, `name` FROM `people` "
     . "WHERE `name` = 'Susan' "
     . "ORDER BY `name` ASC ";

Negative numbers are not permitted as indices.

An indexed array may start with any non-negative number, however all base indices besides 0 are discouraged.

When declaring indexed arrays with the Array function, a trailing space must be added after each comma delimiter to improve readability:

$sampleArray = array(1, 2, 3, 'Zend', 'Studio');

It is permitted to declare multi-line indexed arrays using the "array" construct. In this case, each successive line must be padded with spaces such that beginning of each line is aligned:

$sampleArray = array(1, 2, 3, 'Zend', 'Studio',
                     $a, $b, $c,
                     56.44, $d, 500);

When declaring associative arrays with the Array construct, breaking the statement into multiple lines is encouraged. In this case, each successive line must be padded with white space such that both the keys and the values are aligned:

$sampleArray = array('firstKey'  => 'firstValue',
                     'secondKey' => 'secondValue');

Classes must be named according to Zend Framework's naming conventions.

The brace should always be written on the line underneath the class name.

Every class must have a documentation block that conforms to the PHPDocumentor standard.

All code in a class must be indented with four spaces.

Only one class is permitted in each PHP file.

Placing additional code in class files is permitted but discouraged. In such files, two blank lines must separate the class from any additional PHP code in the class file.

The following is an example of an acceptable class declaration:

/**
 * Documentation Block Here
 */
class SampleClass
{
    // all contents of class
    // must be indented four spaces
}

Member variables must be named according to Zend Framework's variable naming conventions.

Any variables declared in a class must be listed at the top of the class, above the declaration of any methods.

The var construct is not permitted. Member variables always declare their visibility by using one of the private, protected, or public modifiers. Giving access to member variables directly by declaring them as public is permitted but discouraged in favor of accessor methods (set/get).

Functions must be named according to the Zend Framework function naming conventions.

Methods inside classes must always declare their visibility by using one of the private, protected, or public modifiers.

As with classes, the brace should always be written on the line underneath the function name. Space between the function name and the opening parenthesis for the arguments is not permitted.

Functions in the global scope are strongly discouraged.

The following is an example of an acceptable function declaration in a class:

/**
 * Documentation Block Here
 */
class Foo
{
    /**
     * Documentation Block Here
     */
    public function bar()
    {
        // all contents of function
        // must be indented four spaces
    }
}

NOTE: Pass-by-reference is the only parameter passing mechanism permitted in a method declaration.

/**
 * Documentation Block Here
 */
class Foo
{
    /**
     * Documentation Block Here
     */
    public function bar(&$baz)
    {}
}

Call-time pass-by-reference is strictly prohibited.

The return value must not be enclosed in parentheses. This can hinder readability, in additional to breaking code if a method is later changed to return by reference.

/**
 * Documentation Block Here
 */
class Foo
{
    /**
     * WRONG
     */
    public function bar()
    {
        return($this->bar);
    }

    /**
     * RIGHT
     */
    public function bar()
    {
        return $this->bar;
    }
}

Function arguments should be separated by a single trailing space after the comma delimiter. The following is an example of an acceptable invocation of a function that takes three arguments:

threeArguments(1, 2, 3);

Call-time pass-by-reference is strictly prohibited. See the function declarations section for the proper way to pass function arguments by-reference.

In passing arrays as arguments to a function, the function call may include the "array" hint and may be split into multiple lines to improve readability. In such cases, the normal guidelines for writing arrays still apply:

threeArguments(array(1, 2, 3), 2, 3);

threeArguments(array(1, 2, 3, 'Zend', 'Studio',
                     $a, $b, $c,
                     56.44, $d, 500), 2, 3);

Control statements based on the if and elseif constructs must have a single space before the opening parenthesis of the conditional and a single space after the closing parenthesis.

Within the conditional statements between the parentheses, operators must be separated by spaces for readability. Inner parentheses are encouraged to improve logical grouping for larger conditional expressions.

The opening brace is written on the same line as the conditional statement. The closing brace is always written on its own line. Any content within the braces must be indented using four spaces.

if ($a != 2) {
    $a = 2;
}

For "if" statements that include "elseif" or "else", the formatting conventions are similar to the "if" construct. The following examples demonstrate proper formatting for "if" statements with "else" and/or "elseif" constructs:

if ($a != 2) {
    $a = 2;
} else {
    $a = 7;
}

if ($a != 2) {
    $a = 2;
} elseif ($a == 3) {
    $a = 4;
} else {
    $a = 7;
}

PHP allows statements to be written without braces in some circumstances. This coding standard makes no differentiation- all "if", "elseif" or "else" statements must use braces.

Use of the "elseif" construct is permitted but strongly discouraged in favor of the "else if" combination.

Control statements written with the "switch" statement must have a single space before the opening parenthesis of the conditional statement and after the closing parenthesis.

All content within the "switch" statement must be indented using four spaces. Content under each "case" statement must be indented using an additional four spaces.

switch ($numPeople) {
    case 1:
        break;

    case 2:
        break;

    default:
        break;
}

The construct default should never be omitted from a switch statement.

NOTE: It is sometimes useful to write a case statement which falls through to the next case by not including a break or return within that case. To distinguish these cases from bugs, any case statement where break or return are omitted should contain a comment indicating that the break was intentionally omitted.

All documentation blocks ("docblocks") must be compatible with the phpDocumentor format. Describing the phpDocumentor format is beyond the scope of this document. For more information, visit: http://phpdoc.org/

All class files must contain a "file-level" docblock at the top of each file and a "class-level" docblock immediately above each class. Examples of such docblocks can be found below.

Every file that contains PHP code must have a docblock at the top of the file that contains these phpDocumentor tags at a minimum:

/**
 * Short description for file
 *
 * Long description for file (if any)...
 *
 * LICENSE: Some license information
 *
 * @copyright  2008 Zend Technologies
 * @license    http://framework.zend.com/license   BSD License
 * @version    $Id:$
 * @link       http://framework.zend.com/package/PackageName
 * @since      File available since Release 1.5.0
*/

Every class must have a docblock that contains these phpDocumentor tags at a minimum:

/**
 * Short description for class
 *
 * Long description for class (if any)...
 *
 * @copyright  2008 Zend Technologies
 * @license    http://framework.zend.com/license   BSD License
 * @version    Release: @package_version@
 * @link       http://framework.zend.com/package/PackageName
 * @since      Class available since Release 1.5.0
 * @deprecated Class deprecated in Release 2.0.0
 */

Every function, including object methods, must have a docblock that contains at a minimum:

It is not necessary to use the "@access" tag because the access level is already known from the "public", "private", or "protected" modifier used to declare the function.

If a function/method may throw an exception, use @throws for all known exception classes:

@throws exceptionclass [description]