minor punctuation fixes - adding missing commas

guidelines/sc/21/pointer-cancellation.html

@@ -23,6 +23,6 @@ <h4>Pointer Cancellation</h4>
    </dl>
    <p class="note">Functions that emulate a keyboard or numeric keypad key press are considered essential.</p>
 
-  <p class="note">This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).</p>
+  <p class="note">This requirement applies to web content that interprets pointer actions (i.e., this does not apply to actions that are required to operate the user agent or assistive technology).</p>
 
 </section>

guidelines/sc/21/pointer-gestures.html

@@ -6,6 +6,6 @@ <h4>Pointer Gestures</h4>
 
    <p>All <a>functionality</a> that uses multipoint or path-based gestures for operation can be operated with a <a>single pointer</a> without a path-based gesture, unless a multipoint or path-based gesture is <a>essential</a>.</p>
 
-   <p class="note">This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).</p>
+   <p class="note">This requirement applies to web content that interprets pointer actions (i.e., this does not apply to actions that are required to operate the user agent or assistive technology).</p>
 
 </section>

guidelines/sc/22/dragging-movements.html

@@ -6,6 +6,6 @@ <h4>Dragging Movements</h4>
 	<p class="change">New</p>
 
   <p>All <a>functionality</a> that uses a <a>dragging movement</a> for operation can be achieved by a <a>single pointer</a> without dragging, unless dragging is <a>essential</a> or the functionality is determined by the <a>user agent</a> and not modified by the author.</p>
-    <p class="note">This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).</p>
+    <p class="note">This requirement applies to web content that interprets pointer actions (i.e., this does not apply to actions that are required to operate the user agent or assistive technology).</p>
 
  </section>

guidelines/sc/22/focus-appearance.html

@@ -20,6 +20,6 @@ <h4>Focus Appearance</h4>
 
     <p class="note">Examples of sub-components that may receive a focus indicator are menu items in an opened drop-down menu, or focusable cells in a grid.</p>
 
-    <p class="note">Contrast calculations can be based on colors defined within the <a>technology</a> (such as HTML, CSS and SVG). Pixels modified by user agent resolution enhancements and anti-aliasing can be ignored.</p>
+    <p class="note">Contrast calculations can be based on colors defined within the <a>technology</a> (such as HTML, CSS, and SVG). Pixels modified by user agent resolution enhancements and anti-aliasing can be ignored.</p>
 
 </section>

understanding/21/non-text-contrast.html

@@ -470,7 +470,7 @@ <h3>Testing Principles</h3>
 								<li>Test those contrast indicators in each state.</li>
 							</ul>
 						</li>
-						<li>Identify each graphic on the page that includes information required for understanding the content (i.e. excluding graphics which have visible text for the same information, or are decorative) and:
+						<li>Identify each graphic on the page that includes information required for understanding the content (i.e., excluding graphics which have visible text for the same information, or are decorative) and:
 							<ul>
 								<li>Check the contrast of the graphical object against its adjacent colors;</li>
 								<li>If there are multiple colors and/or a gradient, choose the least contrasting area to test;</li>