FEATURE: Mouse button clicks can now be bound in keymaps by using
names like `"LeftClick"` or `"Ctrl-Alt-MiddleTripleClick"`. When bound
to a function, that function will be passed the position of the click
as second argument.

FEATURE: The behavior of mouse selection and dragging can now be
customized with the
[`configureMouse`](http://codemirror.net/doc/manual.html#option_configureMouse)
option.

Issue #4727

Issue #4759

See https://discuss.codemirror.net/t/nested-block-comments-not-displayed-correctly/1253/3

See https://discuss.codemirror.net/t/how-to-check-if-inside-comment/1252

This closes #4691 and is based on an idea by Joel <joel.einbinder@gmail.com>.

This fixes keyword highlighting for CPython and Verilog.

Most cases look like simple typos, other cases suggest misunderstanding of regular expression syntax.

Issue #4754

These properties have been implemented in Firefox, Chrome and Safari.
In addition, the CSS WG has just resolved to move the spec to CR.

Spec: https://drafts.csswg.org/css-align/#property-index

Closes #4739

The property is defined in this spec:
https://drafts.csswg.org/css-ui/#caret-color

It has been recently implemented on Chromium and Firefox.

Issue #4735

Issue #4724

Issue #4733

Issue #4726

Closes #4725

To avoid false negatives due to window scrolling

Avoid duplicates for #4719