Update preallocated-space-placeholders.md

Removed period at wrong place; Rebuild sentence;

Author: JarbasHorst

docs/spfx/extensions/basics/preallocated-space-placeholders.md

@@ -13,7 +13,7 @@ Application customizers can be used to add structures and content on the modern
 > [!NOTE]
 > This feature is only supported in SharePoint Online.
 
-To reduce the page movement, you can **pre-allocate** the extension area already in the server side when page structure is created. This configuration can be applied by using new **HostProperties** property at the **UserCustomAction** collection. which is used in the server side to indicate which application customizers are loaded to the page.
+To reduce the page movement, you can **pre-allocate** the extension area already in the server side when page structure is created. This configuration can be applied by using new **HostProperties** property at the **UserCustomAction** collection to indicate in the server side which application customizers are loaded to the page.
 
 There are two different specific properties, which can be used with the **HostProperties** configuration
 
@@ -76,4 +76,4 @@ There are few considerations to be aware, depending on your implementation:
 * If you have defined a pre-allocation, but application customizer does not create placeholder in the code or is not associated on the page, server side allocated space will remain on the page.
 
 > [!NOTE]
-> HostProperties can be defined also for existing application customizers either modifying site level CustomAction object or by using the **Host Properties** column in the **Tenant Wide Extensions** list at the app catalog site. As this is a server side setting, it can be also applied to extensions which have been built using older SharePoint Framework versions.
+> HostProperties can be defined also for existing application customizers either modifying site level CustomAction object or by using the **Host Properties** column in the **Tenant Wide Extensions** list at the app catalog site. As this is a server side setting, it can be also applied to extensions which have been built using older SharePoint Framework versions.