Revert "Revert "Added `--filter` option.""

This reverts commit 2e5edbb27837372f658b1abbe05371be57415847.

1 files changed, 8 insertions, 0 deletions

diff --git a/README b/README
index bc5d5619d..e85ca1905 100644
--- a/README
+++ b/README
@@ -259,6 +259,14 @@ Reader options
     require different kinds of images.  Currently this option only affects
     the markdown and LaTeX readers.
 
+`--filter=`*PATH*
+:   Specify an executable to be used as a filter transforming the
+    Pandoc AST after the input is parsed and before the output is
+    written.  The executable should read JSON from stdin and write
+    JSON to stdout.  The JSON must be formatted like  pandoc's own
+    JSON input and output.  Filters may be most easily created in Haskell,
+    using the utility function `toJsonFilter` from `Text.Pandoc`.
+
 `--normalize`
 :   Normalize the document after reading:  merge adjacent
     `Str` or `Emph` elements, for example, and remove repeated `Space`s.