public void setRegion(String region) {
        ensureNotFrozen();
        this.region=region;
    }
Returns the identifier telling the layout of the containing section where this section should be placed.
Permissible values, and whether this is mandatory is determined by the particular layout identifier of the parent.
May be null if a placement is not required by the containing layout, or if this is the top-level section.
This is null by default.
container-search/src/main/java/com/yahoo/search/pagetemplates/model/Section.java