Named the margins and padding. Made them functions that can take parameters in the future to allow more complex spacing options in the future.

README.md

@@ -22,6 +22,9 @@ This README is being written.<br>
 
 *Note that today's entry may be updated later today.*
 
+* **26 May 2016**
+	* Two OS X-specific functions have been added: `uiDarwinMarginAmount()` and `uiDarwinPaddingAmount()`. These return the amount of margins and padding, respectively, to give to a control, and are intended for container implementations. These are suitable for the constant of a NSLayoutConstraint. They both take a pointer parameter that is reserved for future use and should be `NULL`.
+
 * **25 May 2016**
 	* uiDrawTextLayout attributes are now specified in units of *graphemes* on all platforms. This means characters as seen from a user's perspective, not Unicode codepoints or UTF-8 bytes. So a long string of combining marker codepoints after one codepoint would still count as one grapheme.
 

darwin/autolayout.m

@@ -18,6 +18,16 @@ NSLayoutConstraint *mkConstraint(id view1, NSLayoutAttribute attr1, NSLayoutRela
 	return constraint;
 }
 
+CGFloat uiDarwinMarginAmount(void *reserved)
+{
+	return 20.0;
+}
+
+CGFloat uiDarwinPaddingAmount(void *reserved)
+{
+	return 8.0;
+}
+
 // this is needed for NSSplitView to work properly; see http://stackoverflow.com/questions/34574478/how-can-i-set-the-position-of-a-nssplitview-nowadays-setpositionofdivideratind (stal in irc.freenode.net/#macdev came up with the exact combination)
 // turns out it also works on NSTabView and NSBox too, possibly others!
 // and for bonus points, it even seems to fix unsatisfiable-constraint-autoresizing-mask issues with NSTabView and NSBox too!!! this is nuts
@@ -31,7 +41,7 @@ static CGFloat margins(int margined)
 {
 	if (!margined)
 		return 0.0;
-	return 20.0;		// TODO named constant
+	return uiDarwinMarginAmount(NULL);
 }
 
 void singleChildConstraintsEstablish(struct singleChildConstraints *c, NSView *contentView, NSView *childView, BOOL hugsTrailing, BOOL hugsBottom, int margined, NSString *desc)

darwin/box.m

@@ -147,7 +147,7 @@ struct uiBox {
 {
 	if (!self->padded)
 		return 0.0;
-	return 8.0;		// TODO named constant
+	return uiDarwinPaddingAmount(NULL);
 }
 
 // TODO something about spinbox hugging

ui_darwin.h

@@ -200,6 +200,10 @@ _UI_EXTERN BOOL uiDarwinShouldStopSyncEnableState(uiDarwinControl *, BOOL);
 // TODO document
 _UI_EXTERN void uiDarwinNotifyEdgeHuggingChanged(uiDarwinControl *);
 
+// TODO document
+_UI_EXTERN CGFloat uiDarwinMarginAmount(void *reserved);
+_UI_EXTERN CGFloat uiDarwinPaddingAmount(void *reserved);
+
 #ifdef __cplusplus
 }
 #endif