PHP & Case Sensitivity

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Answer 1

FYI

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Case sensitive (both user-defined and PHP defined)

• variables
• constants
• array keys
• class properties
• class constants

Case insensitive (both user defined and PHP defined)

• functions
• class constructors
• class methods
• keywords and constructs (if, else, null, foreach, echo etc.)

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In php.net

Basics

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 underscores, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_x7f-xff][a-zA-Z0-9_x7f-xff]*'

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Some useful Links

1. Userland Naming Guide
2. Why are functions and methods in PHP case-insensitive?
3. Are PHP functions case sensitive?
4. Are PHP keywords case-sensitive?
5. Is PHP function names case-sensitive or not?
6. Source of PHP Case Sensitive