数学 ML MO 使用

Math ML MO uses

以下代码片段在 Math ML 文件中的作用是什么?我删除了这些行,它对我来说仍然很好用。

<mo>&#8289;</mo>
<mo>&#8290;</mo>
<mo>&#63449;</mo>

回答他们中的任何一个或只是让我知道他们是什么将不胜感激。

前两个是&#8289; function application and &#8290; invisible times. They help indicate semantic information, see this Wikipedia entry

最后一个,&#63449;, could be anything since it lies in the Unicode Private Use Area which is provided so that font developers can store glyphs that do not correspond to regular Unicode positions. (Unless it's a typo and really 6349是汉字。)