PHP 中首字母大小写处理难题，lcfirst 函数可以怎么解决？

<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// 前置与文章内容无关的代码示例</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">placeholderFunction</span></span><span>(</span><span><span class="hljs-params"></span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"这是前置示例代码，与文章内容无关。"</span></span><span>;
}
</span><span><span class="hljs-title function_ invoke__">placeholderFunction</span></span><span>();
</span><span><span class="hljs-meta">?></span></span><span>

<hr>

</span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// 文章正文开始</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"<h1>PHP 中首字母大小写处理难题，lcfirst 函数可以怎么解决？</h1>"</span></span><span>;

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"<p>在 PHP 编程中，经常会遇到需要对字符串首字母进行大小写处理的情况。例如，一个字符串的首字母需要小写以符合某些命名规范，或者在处理用户输入时需要统一格式。</p>"</span></span><span>;

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"<h2>问题描述</h2>"</span></span><span>;
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"<p>很多初学者会发现，虽然有 <code>strtoupper

\$str = 'HelloWorld';
\$newStr = lcfirst(\$str);
echo \$newStr; // 输出 'helloWorld'

\$str = '中文测试';
\$firstChar = mb_substr(\$str, 0, 1, 'UTF-8');
\$rest = mb_substr(\$str, 1, null, 'UTF-8');
\$newStr = mb_strtolower(\$firstChar, 'UTF-8') . \$rest;
echo \$newStr; // 输出 '中文测试'（首字母小写处理）