Added docs around IMemberPartialViewCacheInvalidator

13/umbraco-cms/reference/cache/imemberpartialviewcacheinvalidator.md

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+# Partial view cache refresher for members
+
+This section describes the `IMemberPartialViewCacheInvalidator` interface, what it's default implementation does and how to customize it.
+
+## What is an IMemberPartialViewCacheInvalidator?
+
+This interface is used to isolate the logic that invalidates parts of the partial view cache when a member is updated.
+
+## Why do we need to partially invalidate the partial view cache?
+
+Razor templates showing data retrieved from a member object can be cached as partial views via:
+
+
+## Where is it used?
+
+This interface is called from the member cache refresher (`MemberCacheRefresher`) which is invoked every time a member is updated.
+
+## Details of the default implementation
+
+Razor template partials are cached through a call to `Html.CachedPartialAsync` with `cacheByMember` set to `true`. This will append the id of the currently logged in member with a marker to the partial view cache key.  For example, `-m1015-`. 
+
+When the `ClearPartialViewCacheItems` method is called it will clear all cache items that match the marker for the updated members.
+
+Since it is possible to call the `Html.CachedPartialAsync` with `cacheByMember` set to `true` while there is no member logged in, it will also clear all cache items with an empty member marker (i.e. `-m-`)
+
+## Customizing the implementation
+
+You can replace the default implementation by removing it and registering your own in a composer.
+
+```csharp
+public class ReplaceMemberCacheInvalidatorComposer : IComposer
+{
+    public void Compose(IUmbracoBuilder builder)
+    {
+        builder.Services.AddUnique<IMemberPartialViewCacheInvalidator, MyCustomMemberPartialViewCacheInvalidator>();
+    }
+}
+```

16/umbraco-cms/reference/cache/imemberpartialviewcacheinvalidator.md

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+# ICacheRefresher
+
+This section describes what IMemberPartialViewCacheInvalidator is, what it's default implementation does and how to customize it.
+
+## What is an IMemberPartialViewCacheInvalidator
+
+This interface is used to isolate the logic that needs to run to invalidate parts of the PartialView cache when a member is updated
+
+## Why do we need to partialy invalidate the partialView cache
+
+Since some of the razor templates might show data that is retrieved from a member object and those templates might be cached by using the partial caching mechanism (i.e. `@await Html.CachedPartialAsync("member",Model,TimeSpan.FromDays(1), cacheByMember:true)`), we need to remove those cached partials when a member is updated.
+
+## Where is it used
+
+This interface is called from the MemberCacheRefresher which is called every time a member is updated.
+
+## Details of the implementation
+
+When a razor template partial is cached trough `Html.CachedPartialAsync` and `cacheByMember` is set to `true`, the extension method will append the memberId of the currently logged in member and a marker (i.e. `-m1015-`) to the partialView chachekey.
+When the `ClearPartialViewCacheItems` method is called it will clear all PartialView cacheItems that have the memberId marker for all passed in members.
+Since it is possible to call the `Html.CachedPartialAsync` with `cacheByMember` set to `true` while there is no member logged in, it will also clear all cache items with an empty member marker (i.e. `-m-`)
+
+## Customizing the implementation
+
+You can replace the default implementation like usual by removing the default and registering your own in a composer.
+
+```csharp
+public class ReplaceMemberCacheInvalidatorComposer : IComposer
+{
+    public void Compose(IUmbracoBuilder builder)
+    {
+        builder.Services.AddUnique<IMemberPartialViewCacheInvalidator, MyCustomMemberPartialViewCacheInvalidator>();
+    }
+}
+```