Jekyll/Liquid output a period/range

period.liquid

{%- assign start = include.start %}
{%- assign end = include.end %}
{%- assign startMonth = start | date: '%b' %}
{%- assign endMonth = end | date: '%b' %}
{%- assign sameMonthStartFmt = include.same_month_start_fmt | default: '%d' -%}
{%- assign sameMonthEndFmt = include.same_month_end_fmt | default: "%d %b '%y" -%}

{%- if startMonth == endMonth -%}
  <time datetime="{{ start | date: '%Y-%m-%d' }}">
    {{- start | date: sameMonthStartFmt -}}
  </time>&ndash;<time datetime="{{ end | date: '%Y-%m-%d' }}">
    {{- end | date: sameMonthEndFmt -}}
  </time>
{%- else -%}
  <time datetime="{{ start | date: '%Y-%m-%d' }}">
    {{- start | date: '%d %b' -}}
  </time>&ndash;{{--}}
  <time datetime="{{ end | date: '%Y-%m-%d' }}">
    {{- end | date: '%d %b %Y' -}}
  </time>
{%- endif -%}