'Render the source line indicated by C{self.frame} and several
surrounding lines.  The active line will be given a I{class} of
C{"snippetHighlightLine"}.  Other lines will be given a I{class} of
C{"snippetLine"}.'

@renderer
def sourceLines(self, request, tag):

    for (lineNumber, sourceLine) in self._getSourceLines():
        newTag = tag.clone()
        if (lineNumber == self.frame[2]):
            cssClass = 'snippetHighlightLine'
        else:
            cssClass = 'snippetLine'
        loader = TagLoader(newTag(**{'class': cssClass}))
        (yield _SourceLineElement(loader, lineNumber, sourceLine))
