Rewrite the informative intro to check() to make its behavior clearer.

Author: tabatkins

css-color/Overview.bs

@@ -1165,7 +1165,7 @@ HWB Colors: ''hwb()'' function</h2>
 		<img src="images/color-picker.png">
 		<figcaption>
 			This is a screenshot of Chrome's color picker,
-			shown when a user activates an <code class='lang-markup'>&lt;input type='color'></code>.
+			shown when a user activates an <code class='lang-markup'>&lt;input type="color"></code>.
 			The outer wheel is used to select the hue,
 			then the relative amounts of white and black are selected by clicking on the inner triangle.
 		</figcaption>
@@ -1494,7 +1494,7 @@ Specifying Grays: the ''gray()'' functional notation</h2>
 		could actually compute the gray with the specified luminance.
 		The sRGB power curve means that grays are much darker than they "should" be;
 		50% gray has a luminance of .21, for example, rather than .5.
-		
+
 		Reversing luminance to color is easy for grays:
 		if L &lt; .0774, <code>x * 12.92</code>;
 		otherwise, <code>(x ^ (5/12)) * 1.055 - .055</code>.
@@ -1516,36 +1516,36 @@ Specifying Grays: the ''gray()'' functional notation</h2>
 Device-independent Colors: Lab and LCH</h2>
 
 	Physical measurements of a color are typically expressed in a color
-	space created in 1976 by the <abbr title='Commission Internationale 
+	space created in 1976 by the <abbr title='Commission Internationale
 	de l'Eclairage'>CIE</abbr>, Lab. Color conversions from one device
-	to another also use Lab as an intermediate step.  Derived from 
-	human vision experiments, Lab represents the entire range of 
+	to another also use Lab as an intermediate step.  Derived from
+	human vision experiments, Lab represents the entire range of
 	color that humans can see.
 
-	<!-- Simplify by saying Lab throughout rather than CIELab or 
+	<!-- Simplify by saying Lab throughout rather than CIELab or
 	CIE L*a*b*, because that is what people write in practice -->
-	Lab is a rectangular coordinate system with a central Lightness axis. 
+	Lab is a rectangular coordinate system with a central Lightness axis.
 	L=0 is deep black (no light at all) while L=100 is white (with a color
-	temperature of 5000K). Usefully, L=50 is mid gray, by design: the  
+	temperature of 5000K). Usefully, L=50 is mid gray, by design: the
 	Lab color space is intended to be <em>perceptually uniform</em>.
 	The a and b axes convey hue; positive values along the a axis are red
 	while negative values are the complementary color, green. Similarly
-	positive values along the b axis are yellow and negative are the 
-	complementary blue/violet. Desaturated colors have small values 
-	of a and b and are close to the L axis; saturated colors lie far from 
+	positive values along the b axis are yellow and negative are the
+	complementary blue/violet. Desaturated colors have small values
+	of a and b and are close to the L axis; saturated colors lie far from
 	the L axis.
 
 	<!-- because Luv is not widely used nowadays, no need to say LCH(ab)
 	to distinguish from LCH(uv) -->
 	LCH has the same L axis as Lab, but uses polar coordinates C (chroma)
-	and H (hue). C is the geometric distance from the L axis and H 
+	and H (hue). C is the geometric distance from the L axis and H
 	is the angle, in degrees, from the positive a axis.
 
 	<p class='note'>
 	The Lightness axis in Lab should not be confused with the L axis in HSL.
 	For example, in HSL, the sRGB colors blue (#00F) and yellow (#FF0)
 	have the same value of L even though visually, blue is much darker. In
-	Lab, if two colors have the same measured L value, they have 
+	Lab, if two colors have the same measured L value, they have
 	identical visual lightness. HSL and related polar RGB models were
 	developed to give similar usability benefits for RGB that LCH gave
 	to Lab.</p>

css-font-loading/Overview.bs

@@ -12,12 +12,12 @@ Previous Version: https://www.w3.org/TR/2014/WD-css-font-loading-3-20140522/
 Editor: Tab Atkins Jr., Google, http://xanthir.com/contact/
 Former Editor: John Daggett, Mozilla, jdaggett@mozilla.com
 Abstract: This CSS module describes events and interfaces used for dynamically loading font resources.
-Link Defaults: css-fonts-3 (descriptor) src, dom-ls (interface) Event, typedarray (interface) ArrayBuffer/ArrayBufferView
+Link Defaults: css-fonts-3 (descriptor) src, dom (interface) Event, typedarray (interface) ArrayBuffer/ArrayBufferView
 Ignored Terms: EventHandler, InvalidModificationError, WorkerGlobalScope, CanvasProxy, Document, add(), src
 </pre>
 
 <pre class="link-defaults">
-spec:dom-ls; type:interface; text:EventTarget
+spec:dom; type:interface; text:EventTarget
 </pre>
 
 <h2 id="introduction">
@@ -823,12 +823,32 @@ The <code>load()</code> method</h3>
 <h3 id='font-face-set-check'>
 The <code>check()</code> method</h3>
 
-	The {{FontFaceSet/check()}} method of {{FontFaceSet}} will determine whether all fonts in the given font list
-	have been loaded and are available.
-	If all fonts are available,
-	it returns true;
+	The {{FontFaceSet/check()}} method of {{FontFaceSet}} will determine you can "safely"
+	render some provided text with a particular font list,
+	such that it won't cause a "font swap" later.
+	If the given text/font combo will not cause any font loads,
+	and does not rely on currently-loading fonts,
+	this method will return true;
 	otherwise, it returns false.
 
+	<div class=note>
+		Two special cases in this method's behavior should be noted,
+		as they are non-obvious:
+
+		* If the specified fonts exist,
+			but all possible faces are ruled out due to their unicode-range not covering the provided text,
+			the method returns <code>true</code>,
+			as the text will be rendered in the UA's fallback font instead,
+			and won't trigger any font loads.
+		* If none of the specified fonts exist,
+			even tho this is technically similar to the previous case,
+			in that text rendered with that font list would just use the UA fallback font.
+			This is because such a situation is almost certainly either a typo,
+			or the result of changing the name of a downloadable font
+			and forgetting to update all places the old name was used,
+			and an error is more useful than a vacuous <code>true</code>.
+	</div>
+
 	When the <dfn method for="FontFaceSet" lt="check(font, text)|check(font)">check</dfn>(
 	<span data-dfn-for="FontFaceSet/check(font, text)"><dfn argument>font</dfn>, <dfn argument>text</dfn>)</span>
 	method is called,