[css-page-floats] minor language fixes, after comments from Liam

Author: johanneswilm

css-page-floats/Overview.bs

@@ -585,14 +585,14 @@ The 'clear' property</h2>
 
 <h2 id="deferring_floats">Deferring floats</h2>
 
-  A page float can be deferred to another <a>fragmentation container</a> than where
-  the <a>float anchor</a> is placed.
+  Users can influence the placement of a page float by deferring them to another
+  <a>fragmentation container</a> than where the <a>float anchor</a> is placed.
 
   Float deferring assigns an <a>initial float reference</a>, yet float stacking can
   lead page floats being moved to a subsequent <a>fragmentation container</a> if
   their <a>initial float reference</a> lacks the space to host them.
 
-  This new property is introduced to control deferring floats:
+  The 'float-defer' property is introduced to control deferring floats:
 
   <h3 id="float-defer-property">The 'float-defer' property</h3>
 
@@ -631,14 +631,34 @@ The 'clear' property</h2>
         within the given <a>fragmentation context</a>.
 
         A negative integer value indicates that the <a>initial float reference</a> of
-        the page float should be the Nth <a>fragmentation container</a> of the
-        <a>fragmentation context</a>, where N is 1 plus the order number of the last
-        <a>fragmentation container</a> within the given <a>fragmentation context</a> after all
-        previous page floats have been placed plus the value of the `float-defer`
-        property.
+        the page float should be a <a>fragmentation container</a> of the
+        <a>fragmentation context</a>, counting backward from the end, so that -1
+        is the last <a>fragmentation container</a>, -2 is the next-to-last, etc. .
+        In the case of a negative integer value, the <a>initial float reference</a> is the
+        Nth <a>fragmentation container</a> of the <a>fragmentation context</a>, where N is 1
+        plus the order number of the last <a>fragmentation container</a> within the given
+        <a>fragmentation context</a> after all previous page floats have been placed plus
+        the value of the `float-defer` property.
 
         Zero is the same as `none`.
 
+        If the value of the `float-defer` property would cause the <a>initial float
+        reference</a> to be an inexistent <a>fragmentation container</a>, the property
+        is interpreted as if it were zero.
+
+        <p class="note">
+          Negative float-defer values put the initial float reference a certain number
+          to be a certain amount of fragmentation containers from the last fragmentation
+          container at the time of of the placement. Subsequent page float stacking
+          can mean that a page float is being placed in a later fragmentation container
+          (a page float with float-defer set to -3 can end up being placed in the
+          last fragmentation container), and later page floats may mean that new
+          fragmentation containers are added, so that the a fragmentation container
+          that previously was Nth last fragmentation container within a fragmentation
+          context now is the N+Xth last. Additional fragmentation container(s) that
+          are added after the page float was placed, will not cause the page float
+          to be moved.
+
       <dt>last
       <dd>
         The <a>initial float reference</a> is the last <a>fragmentation container</a> within
@@ -725,10 +745,11 @@ The 'clear' property</h2>
     Animatable: no
   </pre>
 
-  This property pushes a float in opposite direction of the where it has been
+  This property pushes a float in direction opposite of the where it has been
   floated with 'float'.
 
-  This property can only influence a page float along an axis it has been floated.
+  This property can only influence a page float along an axis along which it has
+  been floated.
 
   <dl>
     <dt>&lt;percentage></dt>