Not finding elements in xml even when attribute property is present

Question

Given the following XML

 <?xml version="1.0" encoding="utf-8" ?>
 <headtags>
  <tags page-path-from-root="Models/ModelDashboard">
    <tag type="title" value=""></tag>
    <tag type="meta" name="keyword" content=""></tag>
    <tag type="meta" name="description" content=""></tag>
    <tag type="meta" name="author" content=""></tag>
    <tag type="link" rel="canonical" href="" />
    <tag type="meta" property="og:locale" content="en_US" />
     <tag type="meta" property="og:type" content="website" />
    <tag type="meta" property="og:title" content="Model Dashboard" />
    <tag type="meta" property="og:description" content="Dashboard of values for a {model}" />
    <tag type="meta" property="og:site_name" content="Car Collector Data" />
    <tag type="meta" property="article:publisher" content="Group LLC" />
    <tag type="meta" property="article:author" content="me" />       
 </tags>
 <tags page-path-from-root="Identity/Account/Manage/SiteStatus">
   <tag type="title" value=""></tag>
   <tag type="meta" name="keyword" content=""></tag>
   <tag type="meta" name="description" content=""></tag>
   <tag type="meta" name="author" content=""></tag>
   <tag type="link" rel="canonical" href="" />
   <tag type="meta" property="og:locale" content="en_US" />
   <tag type="meta" property="og:type" content="" />
   <tag type="meta" property="og:title" content="" />
   <tag type="meta" property="og:description" content="" />
   <tag type="meta" property="og:url" content="" />
   <tag type="meta" property="og:site_name" content="" />
   <tag type="meta" property="article:publisher" content="" />
   <tag type="meta" property="article:author" content="" />   
 </tags>
</headtags>

The following method works all the way until the last line where it always errors on finding the elements where the property value contains "og:", which there are clearly six. Does the colon have to be escaped? I thought so but removing it, that line still fails on Contains("og")

public List<XElement> GetOpenGraphTagsForPage(string page)
{
   var doc = XDocument.Load(_metaTagXmlFile);
       
  var metaTags =  doc.Descendants("headtags")
                    .Elements("tags")
                  //page value is modeldashboard
                   .Where(u => u.Attribute("page-path-from-root").Value.ToLower().Contains(page))
                  .Elements("tag") //[@type='meta'] didn't work in Xname to eliminate next line...why?
                 .Where(u => u.Attribute("type")?.Value == "meta")
                 .Where(u => u.Attribute("property").Value.Contains("og:"))
                .ToList();

        return metaTags;
    }

Additionally, why doesn't this (the error says "[" character isn't allowed)

.Elements("tag[@type='meta']") 

produce the same result as this

 .Elements("tag") //[@type='meta'] didn't work in Xname to eliminate next line...why?
 .Where(u => u.Attribute("type")?.Value == "meta")

the Xpath in the first one is asking for the same thing

Answer 1

Since no one answered this question, and I finally solved the issue. Here is the answer. I used XPath instead of LINQ.

To create the proper XPath we need to use the contains and starts-with methods within XPath.

 public IEnumerable<XElement> GetOpenGraphTagsForPage(string page)
 {
     var doc = XDocument.Load(_metaTagXmlFile);
     var ogTags = doc.XPathSelectElements($"//headtags//tags[contains(@page-path-from-root, '{page}')]//tag[@type='meta'][starts-with(@property, 'og')]");
       
     return ogTags;
 }

I would still like to know the equivalent LINQ, so please post another answer if you have a solution.