Seeing marks, ideally in the gutter, but maybe as a highlight or something, would be helpful. This apparently existed at one point (https://github.com/vscodevim/Vim//commit/713f30a1a8f4923dfc2e7b0cbceffce78ab83c01#diff-a7723f32fe6b05e135838f84e5c23c0fR870), but decoration options have gotten richer and we can put it under a setting.

Is your feature request related to a problem? Please describe.

As I said here:

In spacemacs you have major-modes, like "python", "markdown", and so on. So for example if you open a .md file, spacemacs will use Markdown mode in that buffer.

When you are using a mode, key bindings under <spc> m o