bs-must-show-regexp is a variable defined in `bs.el'.
Its value is

Regular expression for specifying buffers which must be shown.
A buffer whose name matches this regular expression will be
included in the buffer list.
Note that this variable is temporary: if the configuration is changed
it is reset to nil. Use `bs-must-always-show-regexp' to specify buffers
that must always be shown regardless of the configuration.