diff --git a/searx/search/processors/abstract.py b/searx/search/processors/abstract.py
index d4822fc56..d74616db0 100644
--- a/searx/search/processors/abstract.py
+++ b/searx/search/processors/abstract.py
@@ -138,6 +138,13 @@ class EngineProcessor(ABC):
         return False
 
     def get_params(self, search_query, engine_category):
+        """Returns a set of *request params* or ``None`` if request is not supported.
+
+        Not supported conditions (``None`` is returned):
+
+        - A page-number > 1 when engine does not support paging.
+        - A time range when the engine does not support time range.
+        """
         # if paging is not supported, skip
         if search_query.pageno > 1 and not self.engine.paging:
             return None
diff --git a/searx/search/processors/online_currency.py b/searx/search/processors/online_currency.py
index 6bd891b1d..92398239f 100644
--- a/searx/search/processors/online_currency.py
+++ b/searx/search/processors/online_currency.py
@@ -38,6 +38,9 @@ class OnlineCurrencyProcessor(OnlineProcessor):
     engine_type = 'online_currency'
 
     def get_params(self, search_query, engine_category):
+        """Returns a set of *request params* or ``None`` if search query does not match
+        to :py:obj:`parser_re`."""
+
         params = super().get_params(search_query, engine_category)
         if params is None:
             return None
diff --git a/searx/search/processors/online_dictionary.py b/searx/search/processors/online_dictionary.py
index 77540de9a..fbfc9df8e 100644
--- a/searx/search/processors/online_dictionary.py
+++ b/searx/search/processors/online_dictionary.py
@@ -18,6 +18,8 @@ class OnlineDictionaryProcessor(OnlineProcessor):
     engine_type = 'online_dictionary'
 
     def get_params(self, search_query, engine_category):
+        """Returns a set of *request params* or ``None`` if search query does not match
+        to :py:obj:`parser_re`."""
         params = super().get_params(search_query, engine_category)
         if params is None:
             return None
diff --git a/searx/search/processors/online_url_search.py b/searx/search/processors/online_url_search.py
index 2863be28e..6383fa37f 100644
--- a/searx/search/processors/online_url_search.py
+++ b/searx/search/processors/online_url_search.py
@@ -20,6 +20,9 @@ class OnlineUrlSearchProcessor(OnlineProcessor):
     engine_type = 'online_url_search'
 
     def get_params(self, search_query, engine_category):
+        """Returns a set of *request params* or ``None`` if search query does not match
+        to at least one of :py:obj:`re_search_urls`.
+        """
         params = super().get_params(search_query, engine_category)
         if params is None:
             return None