Some other conventions

The following are some other conventions that are not defined clearly in PSR.

Use the newest PHP version if possible.
When declaring array, item list can be split across multiple lines. Then the following rules must be followed:
- The first item must be put in a new line.
- There must be only one item per line. Each subsequent line is indented once.
- There must be a comma at the last line.
- The mark of ending array declaration (] for [] or ) for array()) must be put in a new line.

// Bad
$a = [$foo,
    $bar
];

// Bad
$a = [
    $foo, $bar,
    $baz,
];

// Bad
$a = [
    $foo,
    $bar
];

// Bad
$a = [
    $foo,
    $bar,];

// Bad
$a = [$foo, $bar,];

// Good
$a = [
    $foo,
    $bar,
];

$a = [$foo, $bar];

When using PHP >= 5.4, use array short syntax. ([] instead of array())

// Good
$a = [];
$b = [
    $key => $value,
    $key2 => $value2,
];

// Bad
$a = array();
$b = array(
    $key => $value,
    $key2 => $value2,
);

Variables MUST be written in camelCase. However, Model's properties can be written in snake_case so they can be the same with columns name in table in database.
Use ' for normal string. Only use " when you have PHP variables inside.

$normalString = 'A String';
$specialString = "This is {$normalString}";

There MUST be one space before and after each operator (such as +, -, *, /, ., >, <, == ...)
To format the year part of a date as yyyy, use Y.