htmlagilitypack identify inconsistancy - xpath

Question

I use htmlagilitypack & xpath.
How can I identify insconsistancy in html. For example:
<table><tr><td>
<b>Car1</b><span>Color123</span>
<bCar2</b><span>Color333</span>
<b>Car3</b><span>Color221</span>
<b>Car4 <span>Color224</span>
<b>Car5</b><span>Color621</span>
</table></tr></td>
Car2 & Car4 bold are broken.
The problem is that i use root.SelectNodes("//b[1]")[Index] and it misses index position2 (Car2) and put on its place Car3 and I don't even know that such thing happened if i don't inspect the results manually. At least, i need to have "empty" position2 (Car2) and a correct position3 (Car3).
HtmlAgility pack can't indetify and fix it automatically. doc.ParseErrors can't identify it.
Can you offer some combination of XPath functions like Substring, Boolean, Concat, Number etc.? I'm not good enough in XPath, but I feel that these functions can help in identifying inconsistancy.
p.s. Html Tidy library can't fix it. It sometimes decides that:
<b>Car4 <span>Color224</span></b>
Which is not the correct fix.

Answer 1

HtmlDocumemt.ParseErrors does contains 3 errors for your example:
- Start tag <b> was not found (because there is a closing b without an opening one)
- Start tag <tr> was not found (because the tr is inside an opening b without a closing one)
- Start tag <td> was not found (same as tr)
In the general case, it's impossible to 1) identify errors the way you want, and 2) much more difficult to fix them. You would have to exactly define what's the expected format.
You can use the Html Agility Pack to identify errors with specific requirements. For example here is a piece of code, that validates your doc, base on the functional requirement that "every child element of a TD must be a B or a SPAN and must not contain more than one grand child element":
HtmlDocument doc = new HtmlDocument();
doc.Load("MyFile.htm");
foreach (HtmlNode childOfTd in doc.DocumentNode.SelectNodes("//td/*"))
{
if ((childOfTd.Name != "b") && (childOfTd.Name != "span") || (childOfTd.ChildNodes.Count > 1))
{
Console.WriteLine("child error, outerHtml=" + childOfTd.OuterHtml);
}
}
To fix this requires raw text access (maybe a Regex, and BTW, a Regex can also identify simple errors) because the Html Agility Pack builds a DOM that does not let you access incorrect syntax nodes, by design.