Rendering of bibentry objects may be done using routines
  modelled after those used by BibTeX.  This function allows environments
  to be created and manipulated to contain those routines.
There are two ways to create a new style environment.  The easiest
  is to set .init = TRUE, in which case the environment will be
  initialized with a copy of the default "JSS" environment.  (This style
  is modelled after the jss.bst style used by the Journal
    of Statistical Software.)  Alternatively, the envir argument
  can be used to specify a completely new style environment.
To find the name of the default style, use getBibstyle(). To
  retrieve an existing style without setting it as the default, use
  bibstyle(style, .default = FALSE).  To modify an existing style,
  specify style and some named entries via ....
  (Modifying the default "JSS" style is discouraged.)  Setting
  style to NULL or leaving it missing will retrieve the
  default style, but modifications will not be allowed.
At a minimum, the environment should contain routines to render each
  of the 12 types of bibliographic entry supported by
  bibentry as well as several other routines
  described below.
  The former must be named formatArticle,
  formatBook, formatInbook, formatIncollection,
  formatInProceedings, formatManual,
  formatMastersthesis, formatMisc, formatPhdthesis,
  formatProceedings, formatTechreport and
  formatUnpublished.  Each of these takes one argument, a single
  unclass'ed entry from the bibentry vector
  passed to the renderer, and should produce a single element character
  vector (possibly containing newlines).
  
The other routines are as follows.  sortKeys, a function to
  produce a sort key to sort the entries, is passed the original
  bibentry vector and should produce a sortable vector of
  the same length to define the sort order.  Finally,
  the optional function cite should have the same argument list
  as utils::cite, and should produce a citation to be used
  in text.
The format method for "bibentry" objects adds a
  field named ".index" to each entry after sorting and before
  formatting.  This is a 1-based index within the complete object that
  can be used in styles that require numbering.  Although the
  "JSS" style doesn't use numbers, it includes a
  fmtPrefix() stub function that may be used to display them.
  See the example below.