[css-inline-3] Define interaction with floats per <https://lists.w3.o…

…rg/Archives/Public/www-style/2017Feb/0050.html>. #360

css-inline-3/Overview.bs

@@ -1233,13 +1233,49 @@ Short paragraphs with initial letters</h4>
 <h4 id="initial-letter-floats">
 Interaction with floats</h4>
 
-	Floats always clear an initial letter when floated to the same side.
-	When floated to the opposite side,
-	they are pushed down to clear the initial letter
-	only if they have specified 'clear' to the affected side
-	or they do not fit without overlapping the initial letter.
+	<a>Initial letters</a> are not <a href="https://www.w3.org/TR/CSS21/visuren.html#floats">floats</a>:
+	they are <a>in-flow</a> <a>inline-level</a> content
+	that belongs to a <a>line box</a>.
+	Therefore:
 
-	Issue: Is this the behavior we want? What if the float is on the same line as the initial letter?
+	<ul>
+		<li>
+			The 'clear' property does not care about <a>initial letters</a>:
+			it neither applies to <a>initial letters</a>
+			nor clears them when applied to nearby floats.
+		<li>
+			Like line boxes or floats,
+			<a>initial letter boxes</a>
+			must not overlap the <a>margin boxes</a>
+			of any floats participating in the same <a>block formatting context</a>.
+			An overlapping <a>initial letter box</a>
+			is shifted inward or downward
+			until either it fits without overlapping
+			or there are no more floats present.
+		<li>
+			If a line box’s start edge shifts or moves down to clear a float,
+			an <a>initial letter</a> originating in it moves with it;
+			likewise if an <a>initial letter</a> shifts inward or moves downward
+			to clear a float,
+			its originating line box and subsequent line boxes
+			shorten and/or move accordingly.
+		<li>
+			If an <a>inline-start</a> float
+			originates in the first line of content
+			adjacent to an <a>initial letter</a>,
+			then it moves past the <a>initial letter</a>
+			towards the containing block edge,
+			exactly as if the <a>initial letter</a> were any other inline-level content.
+
+			However, if such a float originates
+			in subsequent lines of content adjacent to a (sunk) <a>initial letter</a>,
+			then that float must clear the <a>initial letter</a>.
+	</ul>
+
+	See <a href="https://www.w3.org/TR/CSS21/visuren.html#floats">CSS2&sect;9.5</a>
+	for more information about the layout of floats
+	and adjacent content.
+	[[!CSS2]]
 
 <h4 id="intial-letter-breaking">
 Interaction with Fragmentation (Pagination)</h4>