I have a TagBuilder which contains Outer and Inner Elements. How do I traverse to the Input level line , and Add the following as an New attribute?

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<div class="form-group"> <div class="cont label-outside"> <label>Name</label> <div class="group"> <input type="text" required="required" class="focusedOut"> <span class="highlight"></span> <span class="bar"></span> <span class="close-button" onclick="clear()"></span> </div> </div> </div>

If no Tagbuilder/Taghelper method exists, should C# HTML Agility package be utilized to edit tag tree? https://html-agility-pack.net/traversing ; If yes, how to convert Tagbuilder/ or Taghelper Output into Agility Package HTMLDocument?

*This is different from question Add CSS Class to All Tags in TagBuilder, Edit Existing Attribute as this asks to Edit existing attribute. Question here is about Adding New Attribute. See article below :

Why isn't it good to ask multiple questions and answers in one question