Finish drafting section "Discernable and Predictable Keyboard Focus"

[mcking65]

The section Discernable and Predictable Keyboard Focus is incomplete.

This section may benefit from examples and images, potentially on a separate example page.

[carmacleod]

affect vs effect:

1. Authors need to manage events that effect the currently active element
   should be:
   Authors need to manage events that affect the currently active element

2. browsers move focus to the body element, affectively causing a loss of focus within the user interface.
   should be:
   browsers move focus to the body element, effectively causing a loss of focus within the user interface.

[carmacleod]

devistating should be: devastating

[carmacleod]

The beginning of paragraph 4.4 needs to start with a capital letter...
in composite widgets
should be:
In composite widgets

[carmacleod]

Need a lowercase i for the word "in" in the following phrase:
except In Mac OS

[carmacleod]

In section 4.5, note that tabindex=-1 is actually focusable with a mouse click as well as with javascript.
This can take people by surprise, so probably should mention it, i.e.:
tabindex="-1"
The element is not included in the tab sequence but is focusable with element.focus().
should be:
tabindex="-1"
The element is not included in the tab sequence but is focusable with the mouse or element.focus().

For reference, here's tabindex in the HTML spec: https://www.w3.org/TR/html51/editing.html#the-tabindex-attribute
"Positive numbers specify the relative position of the element’s focusable areas in the sequential focus navigation order, and negative numbers indicate that the control is to be unreachable by sequential focus navigation."

[carmacleod]

4.6.2 change "scrolled" to "scroll" in the following sentence:
Move the visual focus indicator and, if necessary, scrolled the active element into view.