Add help for alarm rule TBEL condition expression

ui-ngx/src/app/modules/home/components/alarm-rules/cf-alarm-rule-condition-dialog.component.html

@@ -63,7 +63,9 @@
                         [functionArgs]="functionArgs"
                         [highlightRules]="argumentsHighlightRules"
                         [editorCompleter]="argumentsEditorCompleter"
-                        noValidate="true">
+                        noValidate="true"
+                        [helpPopupStyle]="{ width: '1200px' }"
+                        helpId="alarm-rule/expression_fn">
               <div toolbarPrefixButton
                    class="tb-primary-background tbel-script-lang-chip">{{ 'alarm-rule.expression-type.script' | translate }}
               </div>

ui-ngx/src/assets/help/en_US/alarm-rule/expression_fn.md

@@ -0,0 +1,47 @@
+## Alarm rule condition TBEL script function
+
+The **expression()** function is a user-defined script that enables custom condition expressions using [TBEL](${siteBaseUrl}/docs${docPlatformPrefix}/user-guide/tbel/) on telemetry and attribute data.
+It receives arguments configured in the alarm rule setup, along with an additional `ctx` object that stores `latestTs` and provides access to all arguments.
+
+### Function signature
+
+```javascript
+function expression(ctx, arg1, arg2, ...): boolean
+```
+
+### Supported arguments
+
+There are two types of arguments supported in the alarm rule configuration: attributes and latest telemetry.
+
+These arguments are single values and may be of type: boolean, int64 (long), double, string, or JSON.
+
+### Usage
+
+**Example: Convert temperature from Fahrenheit to Celsius and raise the alarm if the Celsius value is greater than 36**
+
+```javascript
+var temperatureC = (temperatureF - 32) / 1.8;
+return temperatureC > 36;
+```
+
+Alternatively, use `ctx` to access the argument as an object:
+
+```json
+{
+  "temperatureF": {
+    "ts": 1740644636669,
+    "value": 98.7
+  }
+}
+```
+
+You may notice that the object includes both the `value` of an argument and its timestamp as `ts`.
+The `ctx` object also includes the property `latestTs`, which represents the latest timestamp of the arguments telemetry in milliseconds.
+
+Let's modify the expression that converts Fahrenheit to Celsius to also check if the temperature's timestamp is exactly at the start of an hour:
+
+```javascript
+var temperatureC = (ctx.args.temperatureF.value - 32) / 1.8;
+var temperatureTs = ctx.args.temperatureF.ts;
+return temperatureC > 36 && ((temperatureTs / 1000) % 3600) == 0;
+```