string literal
String literals are sequences of zero or more ASCII standard characters between " double quotes ".  For example, in x$ = "mark", x$ is a string variable, while "mark" is a string literal.

Backslash characters are defined for imbedding non-printable characters in literal strings.  The \ and the following character are converted to one character, as summarized in the following table.

\0     0x00     null
\a     0x07     alarm (bell)
\b     0x08     backspace
\d     0x7F     delete
\e     0x1B     escape
\f     0x0C     form-feed
\n     0x0A     newline
\r     0x0D     return
\t     0x09     tab
\v     0x0B     vertical-tab
\\     0x5C     backslash
\'     0x27     single-quote
\"     0x22     double-quote
\      OOO      0oOOO octal value
\xHH   0xHH     hex value 0xHH

In \OOO (octal format), values from \000 to \377 are valid.  \OOO format is initiated by \ followed by an octal digit 0-7, and continues to the first non-octal digit or until three octal digits have been collected.  The most significant bit of \400 through \777 is lost.

In \xHH (hex format), values from \x00 to \xFF are valid. xHH format is initiated by \x and continues to the first non-hex digit or until two hex digits have been collected.

When \ is followed by any non-alphanumeric character, the \ is ignored and the character is included in the string.

When \ is followed by an alphabetic character not shown the preceding table, the backslash is ignored and the character is included in the string.  New backslash characters may be defined in subsequent versions, so undefined backslash characters may result in inconsistent behavior.