But of course, like any immutable system, there are mutable parts (otherwise, we couldn’t create any configuration files). OSTree handles this with “overlays” (actually, we use OverlayFS) that allow a read-write filesystem to be layered on top of the immutable system. For example, the /etc and /var directories are writable, while the rest of the system is read-only.
Since every person is different, there’s no one best ergonomic keyboard layout. The standard QWERTY layout is what most people are used to. The Dvorak, Colemak and Workman layouts rearrange the board to put the more commonly used letters closer to the home-key position. All three are intended to minimize your finger movements. That may indeed feel more comfortable and less fatiguing, but people used to the QWERTY layout will likely need to relearn how to type.，详情可参考WPS官方版本下载
。关于这个话题，91视频提供了深入分析
Roman numerals: glyph reuse by design，更多细节参见同城约会
Number (4): Everything in this space must add up to 4. The answer is 5-3, placed vertically; 1-1, placed horizontally.