It is impossible to serialize structs into JSON objects with keys containing certain characters, most notably commas (in contrast with all other ASCII punctuation, because they are used to separate key name from tag options). This could be corrected by interpreting escape sequences in the tags as if they were double-quoted strings, which is possible since backslash characters are reserved.

1. What version of Go are you using (go version)?
   go version go1.5.1 linux/amd64
2. What operating system and processor architecture are you using (go env)?
3. What did you do?
   Attempted to serialize a struct into a JSON object with fields containing commas: http://play.golang.org/p/2KgYUahN8a
4. What did you expect to see?

{
 "a": "A:a",
 "b": "B:\u0062",
 "\\u0063": "EscapedC:\\u0063",
 ",": "Comma:\u002c",
 "\\u002c": "EscapedComma:\\u002c"
}

1. What did you see instead?

{
 "a": "A:a",
 "b": "B:b",
 "EscapedC": "EscapedC:\\u0063",
 "Comma": "Comma:,",
 "EscapedComma": "EscapedComma:\\u002c"
}