Change "lt", "gt" & "eq"-selectors to accept an unsigned integer index

HTMLKit/CSSSelectorParser.m

@@ -346,9 +346,9 @@
 
 		NSDecimalNumber *number = [[NSDecimalNumber alloc] initWithDecimal:decimal];
 		if ([pseudoClass isEqualToString:@"lt"]) {
-			return ltSelector(number.unsignedIntegerValue);
+			return ltSelector(number.integerValue);
 		} else if ([pseudoClass isEqualToString:@"gt"]) {
-			return gtSelector(number.unsignedIntegerValue);
+			return gtSelector(number.integerValue);
 		} else if ([pseudoClass isEqualToString:@"eq"]) {
 			return eqSelector(number.integerValue);
 		}

HTMLKit/CSSStructuralPseudoSelectors.h

@@ -113,22 +113,23 @@ extern CSSSelector * requiredSelector();
 /**
  Less-than selector, e.g. 'lt(2)'
 
- Selects all elements at an index less than the specified index.
+ Selects all elements at an index less than the specified index. A negative index counts backwards from the last element.
 
  @param index The zero-based index of the element to match.
  @returns A Less-Than selector.
  */
-extern CSSSelector * ltSelector(NSUInteger index);
+extern CSSSelector * ltSelector(NSInteger index);
 
 /**
  Greater-than selector, e.g. 'gt(2)'
 
- Selects all elements at an index greater than the specified index.
+ Selects all elements at an index greater than the specified index. A negative index counts backwards from the 
+ last element.
 
  @param index The zero-based index of the element to match.
  @returns A Greater-Than selector.
  */
-extern CSSSelector * gtSelector(NSUInteger index);
+extern CSSSelector * gtSelector(NSInteger index);
 
 /**
  Equal selector, e.g. 'eq(3)'

HTMLKit/CSSStructuralPseudoSelectors.m

@@ -270,19 +270,31 @@ CSSSelector * requiredSelector()
 
 #pragma mark - Positional
 
-CSSSelector * ltSelector(NSUInteger index)
+CSSSelector * ltSelector(NSInteger index)
 {
 	NSString *name = [NSString stringWithFormat:@":lt(%lu)", (unsigned long)index];
 	return namedBlockSelector(name, ^BOOL(HTMLElement * _Nonnull element) {
-		return [element.parentElement indexOfChildNode:element] < index;
+		NSUInteger elementIndex = [element.parentElement indexOfChildNode:element];
+
+		if (index > 0) {
+			return elementIndex < index;
+		} else {
+			return elementIndex < element.parentElement.childNodesCount - index - 1;
+		}
 	});
 }
 
-CSSSelector * gtSelector(NSUInteger index)
+CSSSelector * gtSelector(NSInteger index)
 {
 	NSString *name = [NSString stringWithFormat:@":gt(%lu)", (unsigned long)index];
 	return namedBlockSelector(name, ^BOOL(HTMLElement * _Nonnull element) {
-		return [element.parentElement indexOfChildNode:element] > index;
+		NSUInteger elementIndex = [element.parentElement indexOfChildNode:element];
+
+		if (index > 0) {
+			return elementIndex > index;
+		} else {
+			return elementIndex > element.parentElement.childNodesCount - index - 1;
+		}
 	});
 }