PSR-1 is the basic coding standard. It outlines the rules our code should follow, as seen by the members of PHP-FIG. The standard itself is quite short.

Files MUST use only <?php and <?= tags. At one time, PHP supported several different tags (<?php ?>, <? ?>, <?= ?>, <% %>, <%= %>, <script language="php"></script>). The use of some depend on the configuration directives short_open_tag (<? ?>) and asp_tags (<% %>, <%= %>). The PHP 7 release removed ASP tags (<%, <%=), and the script tag (<script language="php">) altogether. The use of only <?php ?> and <?= ?> tags is now recommended in order to maximize compatibility.

Files MUST use only UTF-8 without BOM for PHP code. The byte order mark (BOM) is a Unicode character, U+FEFF BYTE ORDER MARK...

PSR-2 is an extension of PSR-1. This means that when talking about PSR-2, the PSR-1 standard is sort of implicitly understood. The difference is that PSR-2 expands beyond basic class and function formatting by enumerating a set of rules on how to format PHP code. The outlined style rules are derived shared similarities across the various PFP-FIG member projects.

Code MUST follow a coding style guide PSR (PSR-1). Goes to say that every PSR-2 code is implicitly PSR-1 compliant.

Code MUST use 4 spaces for indenting, not tabs. The spaces versus tabs dilemma is quite an old one in the programming world. There are those who the PHP-FIG group voted for the use of spaces, whereas 4 spaces represent what is usually a single tab indent. The benefit of a space over a tab is consistency. Whereas, a tab could show up as a different number of columns depending...

Logging different type of events is a common practice for applications. While one application might categorize these types of events into errors, informational events, and warnings, others might throw in more elaborate levels of severity logging. The same goes for the actual format of the log message itself. Goes to say that every application might easily have its own flavor of logging mechanism. This stands in a way of interoperability.

The PSR-3 standard sets out to fix this by defining a standard for the actual logger interface. Such a standardized interface then enables us to write PHP application logs in a simple and universal way.

The syslog protocol (RFC 5424), defined by Internet Engineering Task Force (IETF), differentiates the following eight severity levels:

• emergency: This states the system is unusable
• alert: This states action must be taken...

To this date, the PHP-FIG group has released two autoloading standards. Predating PSR-4 was PSR-0. It was the first standard released by the PHP-FIG group. Its class naming had certain backward compatibility features aligned with an even older PEAR standard. Whereas, each level of the hierarchy was separated with a single underscore, indicating pseudo-namespaces and directory structure. The PHP 5.3 release then brought official namespace support to the language. PSR-0 allowed both the old PEAR underscore mode and the use of the new namespace notation. Allowing the underscores for some time to follow eased the transition to namespaces and encouraged wider adoption. Pretty soon, Composer came on the scene.

Performance issues are the ever-hot topic of application development. The effects of poorly performing applications can sometimes have serious financial impact. Back in 2007, Amazon reported a 100 ms increase in https://www.amazon.com/ load time and their sales decreased by 1%. Several studies have also shown that nearly half of the users are likely to abandon the website if the page load time is over 3 seconds. To address the performance issues, we look into caching solutions.

Both browsers and servers allow caching of various resources, such as images, web pages, CSS/JS files. Sometimes, however, this is not enough as we need to be able to control the caching of various other bits on the application level, such as objects themselves. Over time, various libraries rolled out their own caching solutions. This made it tough for developers, as...