at json docs i didn't found a specific encode to c1c2c3c4c5c6....

at http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf

---

9 String
A string is a sequence of Unicode code points wrapped with quotation marks (U+0022). All characters may be placed within the quotation marks except for the characters that must be escaped:

quotation mark (U+0022),
reverse solidus (U+005C),
and the control characters U+0000 to U+001F.

There are two-character escape sequence representations of some characters.
\" represents the quotation mark character (U+0022).
\\ represents the reverse solidus character (U+005C).
\/ represents the solidus character (U+002F).
\b represents the backspace character (U+0008).
\f represents the form feed character (U+000C).
\n represents the line feed character (U+000A).
\r represents the carriage return character (U+000D).
\t represents the character tabulation character (U+0009).

So, for example, a string containing only a single reverse solidus character may be represented as "\\". Any code point may be represented as a hexadecimal number. The meaning of such a number is determined by ISO/IEC 10646. If the code point is in the Basic Multilingual Plane (U+0000 through U+FFFF), then it may be represented as a six-character sequence: a reverse solidus, followed by the lowercase letter u, followed by four hexadecimal digits that encode the code point. Hexadecimal digits can be digits (U+0030 through U+0039) or the hexadecimal letters A through F in uppercase (U+0041 through U+0046) or lowercase (U+0061 through U+0066). So, for example, a string containing only a single reverse solidus character may be represented as "\u005C".
The following four cases all produce the same result:

 "\u002F" "\u002f" "\/" "/"

To escape a code point that is not in the Basic Multilingual Plane, the character is represented as a twelvecharacter sequence, encoding the UTF-16 surrogate pair. So for example, a string containing only the G clef character (U+1D11E) may be represented as "\uD834\uDD1E".