From f3a027915cd7dc614d2cff35648246b4b9df1fc3 Mon Sep 17 00:00:00 2001
From: Tim Diggins <tim@red56.uk>
Date: Wed, 5 Oct 2022 12:11:42 +0100
Subject: [PATCH] add a couple of examples for custom filters, including
 registration. (#1098)

relates to #1089
---
 REFERENCE.md | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/REFERENCE.md b/REFERENCE.md
index 6f52690a..cd0ac403 100644
--- a/REFERENCE.md
+++ b/REFERENCE.md
@@ -1201,6 +1201,44 @@ default. This filter is implemented using Tilt.
 You can also define your own filters.
 `Haml::Filters::YourCustomFilter#compile` should return
 [a Temple expression](https://github.com/judofyr/temple/blob/master/EXPRESSIONS.md).
+
+The simplest example of a filter might be something like:
+
+```ruby
+class HelloFilter < Haml::Filters::Base
+  def compile(_node)
+    [:static, "hello world"]
+  end
+end
+
+Haml::Filters.registered[:hello] ||= HelloFilter
+```
+
+A more complex complex example
+
+```ruby
+class BetterFilter < Haml::Filters::Base
+  def compile(node)
+    temple = [:multi]
+    temple << [:static, "hello "]
+    temple << compile_text(node.value[:text])
+    temple << [:static, " world"]
+    temple
+  end
+
+  private
+  def compile_text(text)
+    if ::Haml::Util.contains_interpolation?(text)
+      [:dynamic, ::Haml::Util.unescape_interpolation(text)]
+    else
+      [:static, text]
+    end
+  end
+end
+
+Haml::Filters.registered[:better] ||= BetterFilter
+```
+
 See {Haml::Filters} for examples.
 
 ## Multiline: `|` {#multiline}