import re


def highlight(text, phrase, hilighter='<strong class="hilight">\\1</strong>'):
    """
    Highlights the ``phrase`` where it is found in the ``text``
    
    The highlighted phrase will be surrounded by the hilighter, by default::
    
        <strong class="highlight">I'm a highlight phrase</strong>
    
    ``highlighter``
        Defines the highlighting phrase. This argument should be a single-quoted string
        with ``\\1`` where the phrase is supposed to be inserted.
        
    Note: The ``phrase`` is sanitized to include only letters, digits, and spaces before use.
    """
    if not phrase or not text:
        return text
    return re.sub(re.compile('(%s)' % re.escape(phrase)), hilighter, text, re.I)