How to parse any content which was added after the working out filter 'the_content'

How to parse any content which was added after the working out filter 'the_content'?

For example I have html structure of the simple page that i was created via Worpdress Admin Dashboard -> Pages -> Add New Page:

div id="content" class="site-content"
    div class="wrap"
        div id="primary" class="content-area"
            main id="main" class="site-main" role="main"
                article id="post-20" class="post-20 page type-page status-publish hentry"
                    header class="entry-header"
                        h1 class="entry-title"Some page/h1
                        span class="edit-link"
                            a class="post-edit-link" href="http://wp.loc/wp-admin/post.php?post=20amp;action=edit"Edit
                                span class="screen-reader-text" "Some page"/span
                            /a
                        /span 
                    /header!-- .entry-header --
                    div class="entry-content"
                    /div!-- .entry-content --
                /article!-- #post-## --

            /main!-- #main --
        /div!-- #primary --
    /div!-- .wrap --
/div

After that with some code i add anything to the page.php of my theme. For example:

    ul
        liSome content after working out "the_content" filter/li
        liSome text/li
        liSome text/li
        liSome text/li
        liSome text/li
    /ul

After that i get this page:

div id="content" class="site-content"
    div class="wrap"
        div id="primary" class="content-area"
            main id="main" class="site-main" role="main"
                article id="post-20" class="post-20 page type-page status-publish hentry"
                    header class="entry-header"
                        h1 class="entry-title"Some page/h1
                        span class="edit-link"
                            a class="post-edit-link" href="http://wp.loc/wp-admin/post.php?post=20amp;action=edit"Edit
                                span class="screen-reader-text" "Some page"/span
                            /a
                        /span
                    /header!-- .entry-header --
                    div class="entry-content"
                    /div!-- .entry-content --
                /article!-- #post-## --

            /main!-- #main --
        /div!-- #primary --
    /div!-- .wrap --

    ul
        liSome content after working out "the_content" filter/li
        liSome text/li
        liSome text/li
        liSome text/li
        liSome text/li
    /ul
/div

So, when i call filter 'the_content' i get just this:

div id="content" class="site-content"
div class="wrap"
    div id="primary" class="content-area"
        main id="main" class="site-main" role="main"
            article id="post-20" class="post-20 page type-page status-publish hentry"
                header class="entry-header"
                    h1 class="entry-title"Some page/h1
                    span class="edit-link"
                        a class="post-edit-link" href="http://wp.loc/wp-admin/post.php?post=20amp;action=edit"Edit
                            span class="screen-reader-text" "Some page"/span
                        /a
                    /span 
                /header!-- .entry-header --
                div class="entry-content"
                /div!-- .entry-content --
            /article!-- #post-## --

        /main!-- #main --
    /div!-- #primary --
/div!-- .wrap --

I need to concatenate $content and the content that was added after working out "the_content" filter. I think that i need to use Dom Parser for this. Any suggestions?