OptionalhighOptionallowLow column. Default 'low'.
OptionalmaCentre-line moving average — any of the shared MaType menu.
Default 'trima'.
OptionalpercentBand half-width as a percent of the centre line. Default 1.
(envelope spells the same quantity percent; see the docstring.)
OptionalperiodCentre-line look-back in bars. Default 10.
OptionalprefixColumn-family prefix — appends ${prefix}Middle / ${prefix}Upper /
${prefix}Lower. Default 'hlb'.
High column. Default
'high'.