assertThat(stringPrep("\u2ff0")).isNull()
    assertThat(stringPrep("\u2ffb")).isNull()
  }

  @Test fun prohibitionChangeDisplayPropertiesOrDeprecated() {
    assertThat(stringPrep("\u0340")).isNull() // COMBINING GRAVE TONE MARK
    assertThat(stringPrep("\u200e")).isNull() // LEFT-TO-RIGHT MARK
    assertThat(stringPrep("\u206e")).isNull() // NATIONAL DIGIT SHAPES
    assertThat(stringPrep("\u206f")).isNull() // NOMINAL DIGIT SHAPES
  }

0209          ; valid                                  # 1.1  LATIN SMALL LETTER I WITH DOUBLE GRAVE
020A          ; mapped                 ; 020B          # 1.1  LATIN CAPITAL LETTER I WITH INVERTED BREVE
020B          ; valid                                  # 1.1  LATIN SMALL LETTER I WITH INVERTED BREVE
020C          ; mapped                 ; 020D          # 1.1  LATIN CAPITAL LETTER O WITH DOUBLE GRAVE

   0340; COMBINING GRAVE TONE MARK
   0341; COMBINING ACUTE TONE MARK
   200E; LEFT-TO-RIGHT MARK
   200F; RIGHT-TO-LEFT MARK
   202A; LEFT-TO-RIGHT EMBEDDING
   202B; RIGHT-TO-LEFT EMBEDDING
   202C; POP DIRECTIONAL FORMATTING
   202D; LEFT-TO-RIGHT OVERRIDE
   202E; RIGHT-TO-LEFT OVERRIDE
   206A; INHIBIT SYMMETRIC SWAPPING
   206B; ACTIVATE SYMMETRIC SWAPPING
   206C; INHIBIT ARABIC FORM SHAPING
   206D; ACTIVATE ARABIC FORM SHAPING