code: @Deprecated
      public static int matchAfter(CharSequence a, CharSequence b, int aIndex, int bIndex) {
          int i = aIndex, j = bIndex;
          int alen = a.length();
          int blen = b.length();
          for (; i < alen && j < blen; ++i, ++j) {
              char ca = a.charAt(i);
              char cb = b.charAt(j);
              if (ca != cb) {
                  break;
              }
          }
          // if we failed a match make sure that we didn't match half a character
          int result = i - aIndex;
          if (result != 0 && !onCharacterBoundary(a, i) && !onCharacterBoundary(b, j)) {
              --result; // backup
          }
          return result;
      }
docs: Find the longest n such that a[aIndex,n] = b[bIndex,n], and n is on a character boundary.
  @deprecated This API is ICU internal only.
  @hide draft / provisional / internal are hidden on Android