String.equalsIgnoreCase - UpperCase v.小写

我正在浏览openjdk，注意到String.equalsIgnoreCase中有一个奇怪的代码路径，特别是方法区域Matches：

if (ignoreCase) {
    // If characters don't match but case may be ignored,
    // try converting both characters to uppercase.
    // If the results match, then the comparison scan should
    // continue.
    char u1 = Character.toUpperCase(c1);
    char u2 = Character.toUpperCase(c2);
    if (u1 == u2) {
        continue;
    }
    // Unfortunately, conversion to uppercase does not work properly
    // for the Georgian alphabet, which has strange rules about case
    // conversion.  So we need to make one last check before
    // exiting.
    if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
        continue;
    }
}

我理解关于调整特定字母表以检查小写相等性的评论，但想知道为什么还要进行大写检查？为什么不只做所有小写？