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...
