{%- if include.source1 == nil -%}
  {%- if include.source0 == nil -%}
    {%- assign __return = include.target -%}
  {%- else -%}
    {%- assign __return = include.source0 -%}
  {%- endif -%}
{%- else -%}
  {%- assign __return = include.source1 -%}
{%- endif -%}