How the DOM works
A browser receives HTML as plain text and parses it into a tree. Every element becomes a node, text and attributes hang off those nodes, and the nesting in the file becomes parent and child relationships. That tree is the Document Object Model, and it is what the page actually is from the moment it loads. The file is only the instructions used to build it.
Two things then keep the DOM and the file apart. The parser repairs problems as it goes, closing tags you left open and moving elements that are not allowed where you put them. And scripts can add, change or delete nodes at any point afterwards. This is the difference between the raw page source, which is the file as sent, and the Elements panel in a browser’s developer tools, which shows the current DOM.
Why the DOM matters
Search engines index the rendered DOM, not the delivered file. So every practical question — is my copy there, can this link be followed, which canonical tag is in force — is a question about the DOM rather than about view-source. Two pages can ship identical HTML and end up with completely different documents once their scripts have run.
Its size matters as well. Every node has to be built, styled, laid out and re-checked whenever something changes, so a page carrying a very large or deeply nested tree responds sluggishly to taps and scrolls. That cost lands hardest on modest Android phones, which is the device most Nepali visitors are holding.
Where the DOM goes wrong
The commonest mistake is debugging the wrong artefact. Someone views the source, sees no content, and concludes the page is broken — or views the Elements panel, sees content, and concludes everything is fine. Neither on its own answers the question. If the source is nearly empty while the page is full, the browser built the content, and the crawler has to do the same work before it can read anything.
Conflicting instructions are the expensive version of this. A canonical tag in the HTML and a different one inserted later by a script leaves the search engine to pick, and a robots directive added after load can be honoured just as a server-delivered one would be. Page builders contribute the other failure: layers of wrapper elements that turn a simple section into a deep, heavy subtree for no visible benefit. Invalid markup adds a quieter trap, because the parser’s repair may place an element somewhere you did not intend, which can detach structured data from the content it was describing.
What to do about it
Ask the question in the right place. To check your own page, open the Elements panel and search it for the text or link you expect. To check what a search engine holds, use the URL Inspection tool in Search Console and read its rendered HTML; where the two disagree, the difference is the bug.
Keep the instructions that decide indexing — the canonical tag, the robots meta tag, the title — in the server response, so nothing can quietly overwrite them later. Flatten needless wrapper elements, especially on templates that repeat a card or a row many times over. Validate the HTML so the parser is not left guessing. None of this is glamorous, but it is where a lot of stubborn technical SEO problems turn out to live.