When a string is literal (contains no variable substitutions), the apostrophe or "single quote" must always 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 encouraged for SQL statements:

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

The above syntax is preferred over escaping apostrophes.

Variable substitution is permitted using either of these two forms:

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

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

For consistency, this form is not permitted:

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

Strings may 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 permitted to break the statement into multiple lines to improve readability. In these cases, each successive line should be padded with whitespace 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 be started with any non-negative number, however this is discouraged and it is recommended that all arrays have a base index of 0.

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

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

It is also permitted to declare multiline indexed arrays using the "array" construct. In this case, each successive line must be padded with spaces such that beginning of each line aligns as shown below:

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

When declaring associative arrays with the array construct, it is encouraged to break the statement into multiple lines. In this case, each successive line must be padded with whitespace such that both the keys and the values are aligned:

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

Classes must be named by following the naming conventions.

The brace is always written on the line underneath the class name ("one true brace" form).

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

Any code within a class must be indented four spaces.

Only one class is permitted per PHP file.

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

This is an example of an acceptable class declaration:

/**
 * Documentation Block Here
 */
class SampleClass
{
    // entire content of class
    // must be indented four spaces
}

Member variables must be named by following the variable naming conventions.

Any variables declared in a class must be listed at the top of the class, prior to declaring any functions.

The var construct is not permitted. Member variables always declare their visibility by using one of the private, protected, or public constructs. Accessing member variables directly by making them public is permitted but discouraged in favor of accessor variables (set/get).

Functions must be named by following the naming conventions.

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

Like classes, the brace is always written on the line underneath the function name ("one true brace" form). There is no space between the function name and the opening parenthesis for the arguments.

Functions in the global scope are strongly discouraged.

This is an example of an acceptable function declaration in a class:

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

NOTE: Passing by-reference is permitted in the function declaration only:

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

Call-time pass by-reference is prohibited.

The return value must not be enclosed in parentheses. This can hinder readability and can also break 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 are separated by a single trailing space after the comma delimiter. This is an example of an acceptable function call for a function that takes three arguments:

threeArguments(1, 2, 3);

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

For functions whose arguments permitted arrays, the function call may include the "array" construct and can be split into multiple lines to improve readability. In these cases, the standards 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 of larger conditionals.

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 four spaces.

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

For "if" statements that include "elseif" or "else", the formatting must be as in these examples:

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


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

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

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

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

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

switch ($numPeople) {
    case 1:
        break;

    case 2:
        break;

    default:
        break;
}

The construct default may 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 in that case. To distinguish these cases from bugs, any case statement where break or return are omitted must contain the comment "// break 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 source code file written for the Zend Framework or that operates with the framework must contain a "file-level" docblock at the top of each file and a "class-level" docblock immediately above each class. Below are examples of such docblocks.

Every file that contains PHP code must have a header block 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  2005 Zend Technologies
 * @license    http://www.zend.com/license/3_0.txt   PHP License 3.0
 * @version    CVS: $Id:$
 * @link       http://dev.zend.com/package/PackageName
 * @since      File available since Release 1.2.0
*/

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  2005 Zend Technologies
 * @license    http://www.zend.com/license/3_0.txt   PHP License 3.0
 * @version    Release: @package_version@
 * @link       http://dev.zend.com/package/PackageName
 * @since      Class available since Release 1.2.0
 * @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" construct used to declare the function.

If a function/method may throw an exception, use @throws:

@throws exceptionclass [description]