PSR-1 is a PHP Standards Recommendation created by the PHP-FIG (Framework Interop Group) that defines basic coding standards for PHP code style and structure to ensure interoperability between different PHP projects and frameworks. Its main purpose is to establish a consistent baseline for PHP code, making it easier to understand and collaborate on projects across the PHP ecosystem. PSR-1, also known as the Basic Coding Standard, includes several key guidelines:

1. File Formatting:

   • All PHP files should use only <?php or <?= tags.
   • Files should use UTF-8 encoding without BOM (Byte Order Mark).

2. Namespace and Class Names:

   • Class names must be declared in StudlyCaps (PascalCase).
   • PHP classes should follow the “one class per file” rule and be defined within namespaces that match the directory structure.

3. Constants, Properties, and Method Naming:

   • Constants should be written in all uppercase letters with underscores (e.g., CONST_VALUE).
   • Method names should follow camelCase.

4. Autoloading:

   • PSR-1 encourages using PSR-4 or PSR-0 autoloading standards to make class loading automatic and avoid manual include or require statements.

PSR-1 is considered a foundational standard, and it works in tandem with PSR-2 and PSR-12, which define more detailed code formatting guidelines. Together, these standards help improve code readability and consistency across PHP projects.