Added docs for on_error

docs/classes.md

@@ -25,12 +25,21 @@ Example:
     Lark(...)
 ```
 
-#### parse(self, text)
+#### parse(self, text, start=None, on_error=None)
 
-Return a complete parse tree for the text (of type Tree)
+Parse the given text, according to the options provided.
+
+Returns a complete parse tree for the text (of type Tree)
 
 If a transformer is supplied to `__init__`, returns whatever is the result of the transformation.
 
+Parameters:
+
+* start: str - required if Lark was given multiple possible start symbols (using the start option).
+
+* on_error: function - if provided, will be called on UnexpectedToken error. Return true to resume parsing. LALR only.
+
+(See `examples/error_puppet.py` for an example of how to use `on_error`.)
 
 #### save(self, f) / load(cls, f)
 
@@ -160,6 +169,8 @@ See the [visitors page](visitors.md)
 
 ## UnexpectedToken
 
+TODO: Explain puppet mechanism (related to on_error)
+
 ## UnexpectedException
 
 - `UnexpectedInput`

docs/features.md

@@ -6,6 +6,7 @@
  - EBNF-inspired grammar, with extra features (See: [Grammar Reference](grammar.md))
  - Builds a parse-tree (AST) automagically based on the grammar
  - Stand-alone parser generator - create a small independent parser to embed in your project.
+ - Flexible error handling by using a "puppet parser" mechanism (LALR only)
  - Automatic line & column tracking (for both tokens and matched rules)
  - Automatic terminal collision resolution
  - Standard library of terminals (strings, numbers, names, etc.)

lark/lark.py

@@ -364,7 +364,7 @@ class Lark(Serialize):
 
         Parameters:
             start: str - required if Lark was given multiple possible start symbols (using the start option).
-            on_error: function - if provided, will be called on UnexpectedToken error. Return true to resume parsing.
+            on_error: function - if provided, will be called on UnexpectedToken error. Return true to resume parsing. LALR only.
 
         Returns a tree, unless specified otherwise.
         """