insert_output

        # Encoding::Converter.insert_output

(from ruby core)
### Implementation from Converter
---
    ec.insert_output(string) -> nil

---

Inserts string into the encoding converter. The string will be converted
to the destination encoding and output on later conversions.

If the destination encoding is stateful, string is converted according
to the state and the state is updated.

This method should be used only when a conversion error occurs.

    ec = Encoding::Converter.new("utf-8", "iso-8859-1")
    src = "HIRAGANA LETTER A is \u{3042}."
    dst = ""
    p ec.primitive_convert(src, dst)    #=> :undefined_conversion
    puts "[#{dst.dump}, #{src.dump}]"   #=> ["HIRAGANA LETTER A is ", "."]
    ec.insert_output("<err>")
    p ec.primitive_convert(src, dst)    #=> :finished
    puts "[#{dst.dump}, #{src.dump}]"   #=> ["HIRAGANA LETTER A is <err>.", ""]

    ec = Encoding::Converter.new("utf-8", "iso-2022-jp")
    src = "\u{306F 3041 3068 2661 3002}" # U+2661 is not representable in iso-2022-jp
    dst = ""
    p ec.primitive_convert(src, dst)    #=> :undefined_conversion
    puts "[#{dst.dump}, #{src.dump}]"   #=> ["\e$B$O$!$H".force_encoding("ISO-2022-JP"), "\xE3\x80\x82"]
    ec.insert_output "?"                # state change required to output "?".
    p ec.primitive_convert(src, dst)    #=> :finished
    puts "[#{dst.dump}, #{src.dump}]"   #=> ["\e$B$O$!$H\e(B?\e$B!#\e(B".force_encoding("ISO-2022-JP"), ""]