[DOCS] Expands transforms docs with CCS info (#70156)

Co-authored-by: Lisa Cawley <lcawley@elastic.co>

docs/reference/rest-api/common-parms.asciidoc

@@ -923,8 +923,12 @@ end::source-transforms[]
 tag::source-index-transforms[]
 The _source indices_ for the {transform}. It can be a single index, an index
 pattern (for example, `"my-index-*"`), an array of indices (for example,
-`["my-index-000001", "my-index-000002"]`), or an array of index patterns (for example,
-`["my-index-*", "my-other-index-*"]`.
+`["my-index-000001", "my-index-000002"]`), or an array of index patterns (for 
+example, `["my-index-*", "my-other-index-*"]`. For remote indices use the syntax 
+`"remote_name:index_name"`.
+
+NOTE: If any indices are in remote clusters then the master node and at least 
+one transform node must have the `remote_cluster_client` node role.
 end::source-index-transforms[]
 
 tag::source-query-transforms[]
@@ -933,7 +937,9 @@ A query clause that retrieves a subset of data from the source index. See
 end::source-query-transforms[]
 
 tag::source-runtime-mappings-transforms[]
-Definitions of search-time runtime fields that can be used by the transform.
+Definitions of search-time runtime fields that can be used by the transform. For 
+search runtime fields all data nodes, including remote nodes, must be 7.12 or 
+later.
 end::source-runtime-mappings-transforms[]
 
 tag::state-transform[]

docs/reference/transform/apis/put-transform.asciidoc

@@ -44,18 +44,17 @@ structure (known as a {dataframe}). The ID for each document in the {dataframe}
 is generated from a hash of the entity, so there is a unique row per entity. For 
 more information, see <<transforms>>.
 
-When the {transform} is created, a series of validations occur to
-ensure its success. For example, there is a check for the existence of the
-source indices and a check that the destination index is not part of the source
-index pattern. You can use the `defer_validation` parameter to skip these
-checks.
-
-Deferred validations are always run when the {transform} is started,
-with the exception of privilege checks. When {es} {security-features} are
-enabled, the {transform} remembers which roles the user that created
-it had at the time of creation and uses those same roles. If those roles do not
-have the required privileges on the source and destination indices, the
-{transform} fails when it attempts unauthorized operations.
+When the {transform} is created, a series of validations occur to ensure its 
+success. For example, there is a check for the existence of the source indices 
+and a check that the destination index is not part of the source index pattern. 
+You can use the `defer_validation` parameter to skip these checks.
+
+Deferred validations are always run when the {transform} is started, with the 
+exception of privilege checks. When {es} {security-features} are enabled, the 
+{transform} remembers which roles the user that created it had at the time of 
+creation and uses those same roles. If those roles do not have the required 
+privileges on the source and destination indices, the {transform} fails when it 
+attempts unauthorized operations.
 
 IMPORTANT: You must use {kib} or this API to create a {transform}. Do not put a
 {transform} directly into any `.transform-internal*` indices using the {es}

docs/reference/transform/limitations.asciidoc

@@ -275,3 +275,13 @@ accessed. If the time field is a {ref}/runtime.html[runtime field], the
 performance impact of calculating field values at query time can significantly 
 slow the {transform}. Use an indexed field as a time field when using 
 {transforms}.
+
+
+[discrete]
+[[transforms-ccs-limitation]]
+=== {transforms-cap} support {ccs} if the remote cluster is configured properly
+
+If you use <<modules-cross-cluster-search,{ccs}>>, the remote cluster must 
+support the search and aggregations you use in your {transforms}. 
+{transforms-cap} validate their configuration; if you use {ccs} and the validation fails, 
+make sure that the remote cluster supports the query and aggregations you use.