This section needs expansion. You can help by adding to it. (talk)(June 2013)
Sandbox:
This section needs expansion. You can help by adding to it. (talk)(June 2013)
Expanded code
Current: '"`UNIQ--templatestyles-00000020-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion'''. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>June 2013</span>)</i></span></div></td></tr></table>
Sandbox: '"`UNIQ--templatestyles-00000021-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion'''. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>June 2013</span>)</i></span></div></td></tr></table>
This section needs expansion with: 1 January 2010. You can help by adding to it. (talk)
Sandbox:
This section needs expansion with: 1 January 2010. You can help by adding to it. (talk)
Expanded code
Current: '"`UNIQ--templatestyles-00000027-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: 1 January 2010. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span></div></td></tr></table>
Sandbox: '"`UNIQ--templatestyles-00000028-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: 1 January 2010. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span></div></td></tr></table>
OK, so there's special code in {{Ambox}} that checks for {{subst:Date}}.
Once I look at this saved page, I see {{subst:DATE}} has actually been changed to "date=June 2013". (C.f. {{subst:CURRENTDATE}}:"03:01, Wednesday June 12, 2013 (UTC)") Note also {{DATE}}:"date={{subst:CURRENTMONTHNAME}} {{subst:CURRENTYEAR}}", which will be identical when I save, but the difference is it isn't substed in the preview until the template page is used (transcribed).
{{Expand section/sandbox|with=Foo bar baz quux|{{subst:DATE}}}}
Old {{{1}}}:
This section needs expansion with: Foo bar baz quux. You can help by adding to it. (talk)(December 2011)
New {{{with}}}:
This section needs expansion with: Foo bar baz quux. You can help by adding to it. (talk)(December 2011)
Expanded code
Old {{{1}}}: '"`UNIQ--templatestyles-00000031-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: Foo bar baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>
New {{{with}}}: '"`UNIQ--templatestyles-00000032-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: Foo bar baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>
Old: '"`UNIQ--templatestyles-00000037-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: *Foo bar *Baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>
New: '"`UNIQ--templatestyles-00000038-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: *Foo bar *Baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>
Old: '"`UNIQ--templatestyles-0000003E-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: *Foo bar *Baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>
New: '"`UNIQ--templatestyles-00000040-QINU`"'<tableclass="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content"role="presentation"><tr><tdclass="mbox-image">[[File:Wiki letter w cropped.svg|20px|alt=[icon]]]</td><tdclass="mbox-text"><divclass="mbox-text-span">This section '''needs expansion''' with: *Foo bar *Baz quux. You can help by [//en.wikipedia.org/w/index.php?title=Template:Expand_section/testcases&action=edit§ion= adding to it].<spanclass="hide-when-compact"> ([[Template talk:Expand section/testcases##|talk]])</span><spanclass='date-container'><i>(<spanclass='date'>December 2011</span>)</i></span></div></td></tr></table>