DOC-6013 Augment's lessons learned from this fix

Author: andy-stark-redis

build/tcedocs/README.md

@@ -259,4 +259,22 @@ The following example shows the `connect` step of a Python example:
 ```
 {{< clients-example set="set_and_get" step="connect" lang_filter="Python" />}}
 ```
+
 The programming language name should match the value in the Hugo configuration file.
+
+#### Language Filter Syntax and Matching
+
+The `lang_filter` parameter accepts a **comma-separated list of exact language names**:
+
+```
+{{< clients-example set="example_id" lang_filter="C#-Sync,C#-Async" />}}
+```
+
+**Important**: Language names must match exactly as they appear in `config.toml`. The matching is **exact**, not substring-based:
+
+- ✅ `lang_filter="C#-Sync,C#-Async"` - Shows only C# sync and async tabs
+- ❌ `lang_filter="C"` - Does NOT match "C#-Sync" or "C#-Async" (exact match only)
+- ✅ `lang_filter="Python,Node.js"` - Shows Python and Node.js tabs
+- ❌ `lang_filter="Python,Node"` - Does NOT match "Node.js" (must use exact name)
+
+**Common pitfall**: If you use a language name that is a substring of another language name (e.g., "C" is a substring of "C#-Sync"), the filter will NOT accidentally match the longer name. Each language in the filter list must match exactly.

build/tcedocs/SPECIFICATION.md

@@ -2140,6 +2140,26 @@ OK
 {{< /clients-example >}}
 ```
 
+### Language Filter Matching Behavior
+
+The `lang_filter` parameter uses **exact matching** on comma-separated language names:
+
+**Matching Logic**:
+1. Split the filter string by commas (e.g., `"C#-Sync,C#-Async"` → `["C#-Sync", "C#-Async"]`)
+2. Trim whitespace from each language name
+3. For each configured language in `config.toml`, check if it exactly matches any value in the filter list
+4. Only include languages that match exactly
+
+**Examples**:
+- `lang_filter="C#-Sync,C#-Async"` → Shows only C# sync and async tabs
+- `lang_filter="Python"` → Shows only Python tab
+- `lang_filter="Python,Node.js"` → Shows Python and Node.js tabs
+- `lang_filter="C"` → Shows only C tab (does NOT match "C#-Sync" or "C#-Async")
+
+**Important**: Language names must match exactly as they appear in `config.toml`. This prevents accidental matches when one language name is a substring of another (e.g., "C" is a substring of "C#-Sync", but they are treated as distinct languages).
+
+**Implementation**: See `layouts/partials/tabbed-clients-example.html` for the matching logic.
+
 
 ## Lessons Learned: Adding the C (hiredis) Client