See also the Userland Naming Guide.
Is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML
Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive. Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.