mock up of last updated guidance

input/intro-notes/StructureDefinition-us-core-average-blood-pressure-notes.md

@@ -1,19 +1,3 @@
 {% include StructureDefinition-us-core-vital-signs-notes.md code2="85354-9" code3="96607-7" %}
 
-<div class="bg-success" markdown="1">
-
-1. **SHOULD** support searching using  **[`patient`](SearchParameter-us-core-observation-patient.html)** and **[`code`](SearchParameter-us-core-observation-code.html)** and **[`_lastUpdated`](SearchParameter-us-core-observation-date.html)** search parameters:
-    - including optional support for *OR* search on `code` (e.g.`code={system|}[code],{system|}[code],...`)
-    - including support for these `date` comparators: `gt,lt,ge,le`
-    - including optional support for *AND* search on `date` (e.g.`date=[date]&date=[date]]&...`)
-
-    `GET [base]/Observation?patient={Type/}[id]&code={system|}[code]{,{system|}[code],...}&_lastUpdated={gt|lt|ge|le}[date]{&date={gt|lt|ge|le}[date]&...}`
-
-    Example:
-
-      1. GET [base]/Observation?patient=1186747&amp;code={{code1}},{{code2}},{{code3}}&amp;_lastUpdated=ge2024-03-19
-
-    *Implementation Notes:* Fetches a bundle of all Observation resources for the specified patient and code(s) based on ***the last time they were changed***. **SHOULD** support search by multiple codes. ([how to search by reference] and [how to search by token] and [how to search by date]. ***See the [General Guidance](guidance.html#searching-using-lastupdated) section for additional guidance on searching using `_lastUpdated`.***)
-</div><!-- new-content -->
-
 {% include link-list.md %}

input/pagecontent/guidance.md

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 ### Searching using lastUpdated
 
 <div class="bg-success" markdown="1">
-👉👉👉 Last_update guidance here.... 👈👈👈
+
+Servers that can accurately populate [`Meta.lastUpdated`](#) **SHOULD** support the [`_lastUpdated`](#) search parameter as defined in the core FHIR specifications. If `Meta.lastUpdated` is populated:
+- Any change in the resource implies a change in `Meta.lastUpdated`; conversely, an unchanged `Meta.lastUpdated` implies no change in the resource.
+- Note to clients that the most recent time does not necessarily reflect changes they can access. A record may change, but the client's view of the resource may not (for example, if the client is not authorized to see the changed data).
+- Servers cannot populate `Meta.lastUpdated` if they cannot update it per the rules in the FHIR core specification.
+- Supporting `Meta.lastUpdated` in a resource does not imply support for searches using the `_lastUpdated` search parameter.
+- Support for searches using the `_lastUpdated` search parameter does not require servers to support `Meta.lastUpdated`; servers can use an alternative method to reliably track changes to an instance.
+- Note to servers that updating the timestamp too frequently is better than missing updates.
+
+<div class="stu-note" markdown="1">
+Many servers are unable to populate the `Meta.lastUpdated` element accurately. However,
+they **SHOULD** expose a method for clients to know if there are new or modified resources since their last polling time and advertise that mechanism in their CapabilityStatement.  Work is in progress to:
+- Define an alternative search parameter that provides similar functionality. (see FHIR-45012 - Extension for tracking changes in facade contexts).
+- Enable Subscriptions for notifications on relevant events as an alternative to search polling.
+</div><!-- stu-note -->
+
 </div><!-- new-content -->
 
 ### Compartment Based Search