added customized filtering examples in logging.rst (#4965)

* added customized filtering examples in logging.rst

* Update logging.rst

* Update docs/topics/logging.rst
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

* Update docs/topics/logging.rst
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

* Update docs/topics/logging.rst
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

* Update docs/topics/logging.rst
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

* Update logging.rst
Co-authored-by: NAdrián Chaves <adrian@chaves.io>

docs/topics/logging.rst

@@ -242,6 +242,47 @@ e.g. in the spider's ``__init__`` method::
 If you run this spider again then INFO messages from
 ``scrapy.spidermiddlewares.httperror`` logger will be gone.
 
+You can also filter log records by :class:`~logging.LogRecord` data. For 
+example, you can filter log records by message content using a substring or
+a regular expression. Create a :class:`logging.Filter` subclass 
+and equip it with a regular expression pattern to
+filter out unwanted messages::
+
+    import logging
+    import re
+    
+    class ContentFilter(logging.Filter):
+        def filter(self, record):
+            match = re.search(r'\d{3} [Ee]rror, retrying', record.message)
+            if match:
+                return False
+                
+A project-level filter may be attached to the root 
+handler created by Scrapy, this is a wieldy way to 
+filter all loggers in different parts of the project
+(middlewares, spider, etc.)::
+
+    import logging
+    import scrapy
+
+    class MySpider(scrapy.Spider):
+        # ...
+        def __init__(self, *args, **kwargs):
+            for handler in logging.root.handlers:
+                handler.addFilter(ContentFilter())
+ 
+Alternatively, you may choose a specific logger 
+and hide it without affecting other loggers::
+
+    import logging
+    import scrapy
+    
+    class MySpider(scrapy.Spider):
+        # ...
+        def __init__(self, *args, **kwargs):
+            logger = logging.getLogger('my_logger')
+            logger.addFilter(ContentFilter())
+            
 scrapy.utils.log module
 =======================