PHP language alphabet

The alphabet of a language refers to the set of all permissible characters that can be used in that language.
The PHP language alphabet includes the following characters:

Letters

Uppercase and lowercase Latin letters from A to z, as well as the underscore (_) character, which is also considered a letter. Uppercase and lowercase letters are interchangeable (case-insensitive);

Digits

Arabic digits: 0 1 2 3 4 5 6 7 8 9;

Single characters

Special single characters: + - ! * / = < > . , : ; $ #;

Brackets

Special paired characters: [ ] ( ) { } ;

Composite characters

Composite characters: < =    > = < >    ( * * ) (  ).

The PHP programming language also supports letters from the Russian alphabet, but it is recommended not to use them in your code, as not all programmers may have a keyboard with a Russian layout.