Identifier is a general term applied to variables, functions, and various other userdefined
objects. There are several properties that PHP identifiers must abide by:
- An identifier can consist of one or more characters and must begin with a letter
or an underscore. Furthermore, identifiers can consist of only letters, numbers,underscore characters, and other ASCII characters from 127 through 255.
- Identifiers are case sensitive. Therefore, a variable named $recipe is different
from a variable named $Recipe, $rEciPe, or $recipE
- Identifiers can be any length. This is advantageous because it enables a
programmer to accurately describe the identifier's purpose via the identifier name
- An identifier name can't be identical to any of PHP's predefined keywords. You
can find a complete list of these keywords in the PHP manual appendix.