Update encoding notices for string literals

src/functions-reference/void_functions.Rmd

@@ -39,8 +39,8 @@ Print the values denoted by the arguments x1 through xN on the output
 message stream. There are no spaces between items in the print, but a
 line feed (LF; Unicode U+000A; C++ literal `'\n'`) is inserted at
 the end of the printed line. The types `T1` through `TN` can be any of
-Stan's built-in numerical types or double quoted strings of ASCII
-characters.
+Stan's built-in numerical types or double quoted strings of characters
+(bytes).
 
 ## Reject statement
 
@@ -60,5 +60,4 @@ arguments x1 through xN on the output message stream. There are no
 spaces between items in the print, but a line feed (LF; Unicode
 U+000A; C++ literal `'\n'`) is inserted at the end of the printed
 line. The types `T1` through `TN` can be any of Stan's built-in
-numerical types or double quoted strings of ASCII characters.
-
+numerical types or double quoted strings of characters (bytes).

src/reference-manual/encoding.Rmd

@@ -25,3 +25,19 @@ is convenient.
 Any content after a block comment open sequence in ASCII (`/*`)
 up to the closing block comment (`*/`) is ignored, and thus may
 also be written in whatever character set is convenient.
+
+## String literals
+
+The raw byte sequence within a string literal is escaped according 
+to the C++ standard. In particular, this means that UTF-8 encoded 
+strings are supported, however they are not tested for invalid byte 
+sequences. A `print` or `reject` statement should properly display 
+Unicode characters if your terminal supports the encoding used in the
+input. In other words, Stan simply preserves any string of bytes between 
+two double quotes (`"`) when passing to C++. On compliant terminals,
+this allows the use of glyphs and other characters from encodings such as
+UTF-8 that fall outside the ASCII-compatible range.
+
+ASCII is the recommended encoding for maximum portability, because it encodes
+the ASCII characters (Unicode code points 0--127) using the same sequence of
+bytes as the UTF-8 encoding of Unicode and common ISO-8859 extensions of Latin.

src/reference-manual/statements.Rmd

@@ -211,14 +211,14 @@ statements of the forms listed in the table above.  The compound
 form is legal whenever the corresponding long form would be legal
 and it has the same effect.*
 
- operation  |   compound  |   unfolded
-:-----------|:------------|:-------------
-addition | `x += y` | `x = x + y`
-subtraction | `x -= y` | `x = x - y`
-multiplication | `x *= y` | `x = x * y`
-division | `x /= y` | `x = x / y`
-elementwise multiplication | `x .*= y` | `x = x .* y`
-elementwise division | `x ./= y` | `x = x ./ y`
+ | operation                  | compound  | unfolded     |
+ | :------------------------- | :-------- | :----------- |
+ | addition                   | `x += y`  | `x = x + y`  |
+ | subtraction                | `x -= y`  | `x = x - y`  |
+ | multiplication             | `x *= y`  | `x = x * y`  |
+ | division                   | `x /= y`  | `x = x / y`  |
+ | elementwise multiplication | `x .*= y` | `x = x .* y` |
+ | elementwise division       | `x ./= y` | `x = x ./ y` |
 
 
 ## Increment log density {#increment-log-prob.section}
@@ -1321,16 +1321,14 @@ step, and the `generated quantities` block once per iteration.
 
 String literals begin and end with a double quote character
 (`"`).  The characters between the double quote characters may be
-the space character or any visible ASCII character, with the exception
-of the backslash character (`\`) and double quote character
-(`"`).  The full list of visible ASCII characters is as follows,
-
-```
-a b c d e f g h i j k l m n o p q r s t u v w x y z
-A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
-0 1 2 3 4 5 6 7 8 9 0 { } [ ] ( ) < >
-~ @ # $ ` ^ & * _ ' - + = | / ! ? . , ; :
-```
+any byte sequence, with the exception of the double quote character.
+
+The Stan interfaces preserve the byte sequences which they receive. 
+The encoding of these byte sequences as characters and their rendering
+as glyphs will be handled by whatever display mechanism is being used to
+monitor Stan's output (e.g., a terminal, a Jupyter notebook, RStudio, etc.).
+Stan does not enforce a character encoding for strings, and no attempt is
+made to validate the bytes as legal ASCII, UTF-8, etc.
 
 
 ### Debug by `print` {-}