{%- if include.source1 == nil -%}

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

{%- else -%}

{%- assign __return = include.source1 -%}

{%- endif -%}