<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def render_title_tag(context, is_og=False):
 """ Returns the title as string or a complete open graph meta tag. """

    request = context['request']
    content = ''

    # Try to get the title from the context object (e.g. DetailViews).
    if context.get('object'):
        try:
            content = context['object'].get_meta_title()
        except AttributeError:
            pass
    elif context.get('meta_tagger'):
        content = context['meta_tagger'].get('title')

    if not content:
        # Try to get the title from the cms page.
        try:
            content = request.current_page.get_page_title()  # Try the `page_title` before the `title of the CMS page.
            if not content:
                content = request.current_page.get_title()
        except (AttributeError, NoReverseMatch):
            pass

    if not is_og:
        return content
    else:
        return mark_safe('<meta property="og:title" content="{content}">'.format(content=content))