chore(guideline): add simple index handling

accessibility-rs/src/engine/rules/wcag_base.rs

@@ -59,6 +59,10 @@ impl Principle {
 pub enum Guideline {
     /// Provide text alternatives for any non-text content so that it can be changed into other forms people need.
     TextAlternatives,
+    /// Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
+    Adaptable,
+    /// Make it easier for users to see and hear content including separating foreground from background.
+    Distinguishable,
     /// Provide ways to help users navigate, find content, and determine where they are.
     Navigable,
     /// Make text content readable and understandable.
@@ -67,8 +71,6 @@ pub enum Guideline {
     Predictable,
     /// Provide users enough time to read and use content.
     EnoughTime,
-    /// Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
-    Adaptable,
 }
 
 impl Guideline {
@@ -77,6 +79,7 @@ impl Guideline {
         match self {
             Guideline::TextAlternatives => "Guideline1_1",
             Guideline::Adaptable => "Guideline1_3",
+            Guideline::Distinguishable => "Guideline1_4",
             Guideline::EnoughTime => "Guideline2_2",
             Guideline::Navigable => "Guideline2_4",
             Guideline::Readable => "Guideline3_1",
@@ -85,13 +88,7 @@ impl Guideline {
     }
     /// the principle index
     pub fn as_index(&self) -> &'static str {
-        match self {
-            Guideline::TextAlternatives => "1_1",
-            Guideline::Adaptable => "1_3",
-            Guideline::EnoughTime => "2_2",
-            Guideline::Navigable => "2_4",
-            Guideline::Readable => "3_1",
-            Guideline::Predictable => "3_2",
-        }
+        let s = self.as_str();
+        &s[9..s.len()]
     }
 }