HTML to Attributed String & Attributed String to HTML

MCTextFormatConverter.h

#import <Foundation/Foundation.h>

@interface MCTextFormatConverter : NSObject

	+ (NSString*) convertTextInResponderToHTML:(UIView<UITextInput>*)view convertSelectionOnly:(BOOL)convertSelectionOnly;

	+ (NSAttributedString*) htmlToAttributedString:(NSString*)html;

@end

MCTextFormatConverter.m

#import "MCTextFormatConverter.h"


typedef UIView<UITextInput> __UITextInputView;

@implementation MCTextFormatConverter

	static UIWebView *_dummyWebView;

	+ (void) configureWebViewDummy {
		if(_dummyWebView) return;
		
		_dummyWebView = [[UIWebView alloc] initWithFrame:(CGRect){ 0, 0, 1, 1 }];
		_dummyWebView.keyboardDisplayRequiresUserAction = false;
		
		[_dummyWebView runJS:@"document.body.contentEditable = true;"];
	}

	+ (void) addWebViewToViewHiearchy {
		UIWindow *window = [UIApplication sharedApplication].keyWindow;
		
		[MCTextFormatConverter configureWebViewDummy];
		
		[window addSubview:_dummyWebView];
	}

	+ (NSString*) convertTextInResponderToHTML:(UIView<UITextInput>*)view convertSelectionOnly:(BOOL)convertSelectionOnly {
		NSString *html;
		UITextRange *formerRange = view.selectedTextRange;
		BOOL wasFirstResponder = view.isFirstResponder;
		
		if(!convertSelectionOnly || !formerRange){
			view.selectedTextRange = [view textRangeFromPosition:view.beginningOfDocument toPosition:view.endOfDocument];
		}
		
		UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
		NSArray *formerItems = pasteboard.items;
		
		[view copy:nil];
		
		// ...
		
		[self addWebViewToViewHiearchy];
		
		[_dummyWebView runJS:@"document.body.focus()"];
		
		[_dummyWebView paste:nil];
		
		[_dummyWebView.superview endEditing:true];
		
		[_dummyWebView removeFromSuperview];
		
		//
		
		html = [_dummyWebView runJS:@"document.body.innerHTML"];
		
		//
		
		[_dummyWebView runJS:@"document.body.innerHTML = ''"];
		
		pasteboard.items = formerItems;
		
		if(wasFirstResponder) [view becomeFirstResponder];
		
		view.selectedTextRange = formerRange;
		
		return html;
	}

	+ (NSAttributedString*) htmlToAttributedString:(NSString*)html {
		NSAttributedString *attributedString =
			[[NSAttributedString alloc] initWithData:[html dataUsingEncoding:NSUnicodeStringEncoding]
										options:@{ NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType } documentAttributes:nil error:nil];
		
		return attributedString;
	}

@end

Very early (rough) implementation, but intended to show proof of concept.