Define a new error LEVEL with PROPERTIES.
The following PROPERTIES constitute an error level:
`:severity SEVERITY'
A number denoting the severity of this level. The higher
the number, the more severe is this level compared to other
levels. Defaults to 0.
The severity is used by `flycheck-error-level-<' to
determine the ordering of errors according to their levels.
`:compilation-level LEVEL'
A number indicating the broad class of messages that errors
at this level belong to: one of 0 (info), 1 (warning), or
2 or nil (error). Defaults to nil.
This is used by `flycheck-checker-pattern-to-error-regexp'
to map error levels into `compilation-mode''s hierarchy and
to get proper highlighting of errors in `compilation-mode'.
`:overlay-category CATEGORY'
A symbol denoting the overlay category to use for error
highlight overlays for this level. See Info
node `(elisp)Overlay Properties' for more information about
overlay categories.
A category for an error level overlay should at least define
the `face' property, for error highlighting. Another useful
property for error level categories is `priority', to
influence the stacking of multiple error level overlays.
`:fringe-bitmap BITMAP'
A fringe bitmap symbol denoting the bitmap to use for fringe
indicators for this level. See Info node `(elisp)Fringe
Bitmaps' for more information about fringe bitmaps,
including a list of built-in fringe bitmaps.
`:fringe-face FACE'
A face symbol denoting the face to use for fringe indicators
for this level.
`:error-list-face FACE'
A face symbol denoting the face to use for messages of this
level in the error list. See `flycheck-list-errors'.
(fn LEVEL &rest PROPERTIES)