rb_econv_substr_append  349 include/ruby/encoding.h VALUE rb_econv_substr_append(rb_econv_t *ec, VALUE src, long byteoff, long bytesize, VALUE dst, int flags);
rb_econv_substr_append 1864 transcode.c        return rb_econv_substr_append(ec, src, 0, RSTRING_LEN(src), dst, flags);
rb_econv_substr_append 1870 transcode.c        return rb_econv_substr_append(ec, src, byteoff, bytesize, Qnil, flags);
rb_econv_substr_append 1876 transcode.c        return rb_econv_substr_append(ec, src, 0, RSTRING_LEN(src), Qnil, flags);