So, the below expression:   first reads the Wikipedia Rebol page and then passes the result to the codice_16 function. Parentheses can be used to change the order of evaluation. Using prefix notation, the usage of parentheses in expressions can be avoided. The simple precedence rules are both an advantage: as well as a disadvantage:  The codice_17 function is preferably used to specify, validate, transform and interpret dialects. It does so by matching "parse expressions" at run time. "Parse expressions" are written in the "parse dialect", which, like the "do dialect", is an expression-oriented sublanguage of the "data exchange dialect". Unlike the "do dialect", the "parse dialect" uses keywords representing operators and the most important nonterminals, infix parsing operators don't have prefix equivalents and use precedence rules ("sequence" has higher precedence than "choice"). Actions can be included to be taken during the parsing process as well and the codice_17 function can be used to process blocks or strings. At the "string parsing" level codice_17 must handle the "low level" parsing, taking into account characters and delimiters. "Block parsing" is higher level, handling the scanning at the level of Rebol values. The parse dialect belongs to the family of grammars represented by the top-down parsing language or the parsing expression grammar (PEG). The main similarity is the presence of the "sequence" and "choice" operators all the family members have. Parse dialect syntax and the similarities between the parse dialect and the PEG are illustrated by this transliteration of a PEG example that parses an arithmetic expression:  Digit: charset [#"0" - #"9"] Value: [some Digit | "(" Expr ")"] Product: [Value any "/"] Value Sum: [Product any "-"] Product Expr: Sum parse/all "12+13" Expr  The official Rebol 2.7.8 implementation is available in several editions ("/Core", "/View", "/Command", "/SDK" and "/IOS"). Both "/Core" and "/View" editions are freely redistributable software. The runtime environment is stored in a single executable file. "Rebol/Core" 2.7.8, the console edition, is about 300 KB and "Rebol/View" 2.7.8, the graphical user interface edition, is about 650 KB in size.