The query string is a sequence of tokens where white space is ignored is ignored unless surrounded by double quotes.
The RPN query is a textual represenation of the Type-1 query as defined by the Z39.50 standard. However, in the text representation as used by YAZ a prefix notation is used, that is the operater precedes the operands. The query string is a sequence of tokens where white space is ignored is ignored unless surrounded by double quotes. Tokens beginning with an at-character (@) are considered operators, otherwise they are treated as search terms.