ɪn mˈoʊst kˈeɪsᵻz ðiːz dɪvˈɛləpt æz tɹˈuː ɛkstˈɛnʃənz ʌv ˈæski, lˈiːvɪŋ ðɪ ɚɹˈɪdʒɪnəl kˈæɹɪktɚmˈæpɪŋ ɪntˈækt, bˌʌt ˈædɪŋ ɐdˈɪʃənəl kˈæɹɪktɚ dˌɛfɪnˈɪʃənz ˈæftɚ ðə fˈɜːst wˈʌnhˈʌndɹɪd twˈɛnti ˈeɪt ˈaɪ.ˈiː., sˈɛvənbˈɪt kˈæɹɪktɚz.
In most cases these developed as true extensions of ASCII, leaving the original character-mapping intact, but adding additional character definitions after the first 128 (i.e., 7-bit) characters.