can contain no value (used for classes) and "_" used to store a modified compiler. In MAPPER (aka BIS), named variables are prefixed with "<" and suffixed with ">" because strings or character values do not require quotes. In mIRC script, identifiers have a "$" sigil, while all variables have a "%" prefixed (regardless of local or global variables or data type). Binary variables are prefixed by an "&". In the MUMPS programming language, "$" precedes intrinsic function names and 'special variable names' (built-in variables for accessing the execution state). "$Z" precedes non-standard intrinsic function names. "$$" precedes extrinsic function names. Routines (used for procedures, subroutines, functions) and global variables (database storage) are prefixed by a caret (^). The last global variable subtree may be referenced indirectly by a caret and the last subscript; this is referred to as a "naked reference". System-wide routines and global variables (stored in certain shared database(s)) are prefixed with ^%; these are referred to as "percent routines" and "percent globals". In Objective-C, string literals preceded with "@" are instances of the object type NSString or, since clang v3.1 / LLVM v4.0, NSNumber, NSArray or NSDictionary. The prefix-@ is also used on the keywords interface, implementation, and end to express the structure of class definitions. Within class declarations and definitions as well, a prefix of - is used to indicate member methods and variables, while prefix + indicates class elements. In the PHP language, which was largely inspired by Perl, "$" precedes any variable name. Names not prefixed by this are considered constants, functions or class names (or interface or trait names, which share the same namespace as classes). PILOT uses "$" for buffers (string variables), "#" for integer variables, and "*" for program labels. Python uses a "@" prefix, called pie syntax, for application of decorators and a "__" prefix, called dunder, for "private" attributes. In Ruby, ordinary variables lack sigils, but "$" is prefixed to global variables, "@" is prefixed to instance variables, and "@@" is prefixed to class variables. Ruby also uses (strictly conventional) suffix sigils: "?" indicates a predicate method returning (usually) a boolean value; and "!" indicates that the method may have a potentially unexpected effect, and needs to be handled with care. In Scheme, by convention, the names of procedures that always return a boolean value usually end in "?". Likewise, the names of procedures that store values into