啊啊啊，原来 position: sticky; 已经早就进入标准的 #CSS 了，而我的《CSS 定位 （Positioning）》这篇文章正好写于标准化的那一年前后……

从这个页面的表格上面学来的：https://exiftool.org/。

偷走了，可以在博客程序页面中的更新历史表格中看到效果。

• https://btxx.org/posts/Please_Make_Your_Table_Headings_Sticky/

维斯百科表格中关于 <table> 的使用的描述：

Common attributes for columns, column groups and row groups

The MediaWiki syntax for tables currently offers no support for specifying common attributes for columns (with the HTML element ‎<col />), column groups (HTML element ‎<colgroup>‎</colgroup>) and row groups (HTML elements ‎<thead>‎</thead>, ‎<tbody>‎</tbody> and ‎<tfoot>‎</tfoot>). Those standard HTML elements are not accepted even in their HTML or XHTML syntax.

All the rows and cells (header or data) of the table are rendered within a single implicit row group (HTML element ‎<tbody>‎</tbody>) without any attributes or styles.### Common attributes for columns, column groups and row groups

The MediaWiki syntax for tables currently offers no support for specifying common attributes for columns (with the HTML element ‎<col />), column groups (HTML element ‎<colgroup>‎</colgroup>) and row groups (HTML elements ‎<thead>‎</thead>, ‎<tbody>‎</tbody> and ‎<tfoot>‎</tfoot>). Those standard HTML elements are not accepted even in their HTML or XHTML syntax.

All the rows and cells (header or data) of the table are rendered within a single implicit row group (HTML element ‎<tbody>‎</tbody>) without any attributes or styles.

不要用 border-collapse: separate;，除非样式写得非常完美，否则带 rowspan 的 tr/td 的 border 会重复出现。不信试试？¹

• 把用 outline 实现的 th 的 border 成文（border-collapse 的情况下）；