add documentation for custom token analysis

docs/develop/ICU-Tokenizer-Modules.md

@@ -52,7 +52,8 @@ the function.
 
 ### The sanitation function
 
-The sanitation function receives a single object with three members:
+The sanitation function receives a single object of type `ProcessInfo`
+which has with three members:
 
  * `place`: read-only information about the place being processed.
    See PlaceInfo below.
@@ -62,7 +63,7 @@ The sanitation function receives a single object with three members:
    is a PlaceName object.
 
 While the `place` member is provided for information only, the `names` and
-`address` lists are meant to be manipulated by the sanitizer. If may add and
+`address` lists are meant to be manipulated by the sanitizer. It may add and
 remove entries, change information within a single entry (for example by
 adding extra attributes) or completely replace the list with a different one.
 
@@ -80,3 +81,20 @@ adding extra attributes) or completely replace the list with a different one.
     rendering:
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         heading_level: 6
+
+## Custom token analysis module
+
+Setup of a token analyser is split into two parts: configuration and
+analyser factory. A token analysis module must therefore implement two
+functions:
+
+::: nominatim.tokenizer.token_analysis.base.AnalysisModule
+    rendering:
+        show_source: no
+        heading_level: 6
+
+
+::: nominatim.tokenizer.token_analysis.base.Analyser
+    rendering:
+        show_source: no
+        heading_level: 6

nominatim/tokenizer/token_analysis/base.py

@@ -12,7 +12,8 @@ from typing import Mapping, List, Any
 from nominatim.typing import Protocol
 
 class Analyser(Protocol):
-    """ Instance of the token analyser.
+    """ The `create()` function of an analysis module needs to return an
+        object that implements the following functions.
     """
 
     def normalize(self, name: str) -> str:
@@ -33,10 +34,31 @@ class AnalysisModule(Protocol):
         """ Prepare the configuration of the analysis module.
             This function should prepare all data that can be shared
             between instances of this analyser.
+
+            Arguments:
+                rules: A dictionary with the additional configuration options
+                       as specified in the tokenizer configuration.
+                normalization_rules: ICU rules for normalization as a string
+                                     that can be used with createFromRules().
+
+            Returns:
+                A data object with the configuration that was set up. May be
+                used freely by the analysis module as needed.
         """
 
     def create(self, normalizer: Any, transliterator: Any, config: Any) -> Analyser:
         """ Create a new instance of the analyser.
             A separate instance of the analyser is created for each thread
             when used in multi-threading context.
+
+            Arguments:
+                normalizer: an ICU Transliterator with the compiled normalization
+                            rules.
+                transliterator: an ICU tranliterator with the compiled
+                                transliteration rules.
+                config: The object that was returned by the call to configure().
+
+            Returns:
+                A new analyzer instance. This must be a class that implements
+                the Analyser protocol.
         """