Identifiers

An identifier is a general term applied to variables, functions, and various other user-defined objects. There are several properties that PHP identifiers must abide by:
•An identifier can consist of one or more characters and must begin with an
alphabetical letter or an underscore. Furthermore, identifiers can only consist
of letters, numbers, underscore characters, and other ASCII characters
from 127 through 255. Consider a few examples:
VALID INVALID
my_function This&that
Size !counter
_someword 4ward
• Identifiers are case sensitive. Therefore, a variable named $recipe is different
from variables named $Recipe, $rEciPe, or $recipE.
• Identifiers can be any length. This is advantageous, as it enables a programmer
to accurately describe the identifier’s purpose via the identifier name.
• Finally, an identifier name can’t be identical to any of PHP’s predefined keywords.