add array support, circling buffer section

doc/specs/#980 - SnapOnOutput.md

@@ -23,27 +23,27 @@ Typical Unix terminals work differently. Rather than disabling the output, they
 
 ## Solution Design
 
-`snapOnOutput` will be a profile-level `ICoreSettings` setting of type enum. It can be set to the following values:
+`SnapOnOutput` will be a profile-level `ICoreSettings` setting of type enum or enum array. It can be set to one or multiple of the following values:
 - `never`: new output does not cause the viewport to update to the bottom of the scroll region
 - `noSelection`: (**default**) new output causes the viewport to update to the bottom of the scroll region **IF** no selection is active
 - `atBottom`: new output causes the viewport to update **IF** the viewport is already at the virtual bottom
 - `always`: new output causes the viewport to update to the bottom of the scroll region
 
 The `TerminalCore` is responsible for moving the viewport on a scroll event. All of the logic for this feature should be handled here.
 
-A new private enum `_snapOnOutput` will be introduced for each of the possible settings values. The `_NotifyScrollEvent()` calls (and nearby code) will be surrounded by conditional checks for the enums above.
-
-`_snapOnOutput` can then be used to determine if the viewport should update given a specific situation.
+A new private enum array `_snapOnOutput` will be introduced to save which of these settings are included. The `_NotifyScrollEvent()` calls (and nearby code) will be surrounded by conditional checks for the enums above. This allows it to be used to determine if the viewport should update given a specific situation.
 
 ## UI/UX Design
 
 The `snapOnOutput` setting is done at a profile-level to be near `snapOnInput`. Additionally, the `never` value seems more valuable when the user can dedicate a specific task to the profile. Such a scenario would be a shell that frequently generates new output (i.e.: a live-generating log), but the user is not necessarily interested in what the latest output is.
 
+The default `snapOnOutput` value will be `[ "noSelection", "atBottom" ]`.
+
 ## Capabilities
 
 ### Accessibility
 
-N/A
+The `UiaRenderer` exposes new content that is rendered to the screen upon a scroll. No additional changes are necessary here.
 
 ### Security
 
@@ -63,20 +63,28 @@ N/A
 
 ## Potential Issues
 
+### Circling the buffer
+If the text buffer fills up, the text buffer begins 'circling'. This means that new output shifts lines of the buffer up to make space. In a case like this, if `snapOnOutput` is set to `never`, the viewport should actually scroll up to keep the same content on the viewport.
+
+In the event that the buffer is circling and the viewport has been moved to the top of the buffer, that content of the buffer is now lost (as the 'Infinite Scrollback' feature does not exist or is disabled). At that point, the viewport will remain at the top of the buffer and the new output will push old output out of the buffer.
+
+### Infinite Scrollback
 See **Future considerations** > **Infinite Scrollback**.
 
 ## Future considerations
 
 ### Extensibility
-The introduction of `std::function<bool(void)> _snapOnOutput` allows for this feature to be enabled/disabled in more complex scenarios. A potential extension would be to introduce a new UI element or keybinding to toggle this feature.
+The introduction of `enum SnapOnOutput` allows for this feature to be enabled/disabled in more complex scenarios. A potential extension would be to introduce a new UI element or keybinding to toggle this feature.
 
-Another would be to introduce a more complex boolean function dependent on the state of the app or the contents of the new output. Consider the output from a large testing suite. A user could create an extension that snaps on output for failing tests or when the testing has concluded.
+Another would be to introduce additional accepted values. Consider the output from a large testing suite. A user could create an extension that snaps on output for failing tests or when the testing has concluded.
 
 ### Infinite Scrollback
 At the time of introducing this, the infinite scrollback feature is not supported. This means that the buffer saves the history up to the `historySize` amount of lines. When infinite scrollback is introduced, the buffer needs to change its own contents to allow the user to scroll beyond the `historySize`. With infinite scrollback enabled and the mutable viewport **NOT** snapping to new output, the `TerminalCore` needs to keep track of...
 - what contents are currently visible to the user (in the current location of the mutable viewport)
 - how to respond to a user's action of changing the location of the mutable viewport (i.e.: snapOnInput, scroll up/down)
 
+The `TermControl`'s scrollbar will abstract this issue away. As the viewport moves, really we're just presenting content that was saved to the text buffer.
+
 ### Private Mode Escape Sequences
 There are a couple of private mode escape sequences that some terminals use to control this kind of thing. Mode 1010, for example, snaps the viewport to the bottom on output, whereas Mode 1011 spans the viewport to the bottom on a keypress.