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Intelephense
Intelephense is a high performance, cross platform PHP language server adhering to the Language Server Protocol (LSP).
When paired with an LSP capable editor it provides an essential set of code intelligence features that give a PHP developer a productive and rich editing experience.
This is proprietary software released to end users under a "freemium" model. Many of the features are provided free of charge. Access to all current and future features can be obtained by purchasing a licence key at https://intelephense.com.