Use {{:PAGENAME}} to transclude a mainspace page. (If you don't use a colon, it calls a template instead.)
This doesn't automatically include a header, so you may want a level 1 header, either on the calling or transcluded page, by adding a single "=" either side of the title, on its own line. (The padding space is optional - i.e. "= Title =" and "=Title=" each on their own line, no quote marks, give an identical output.)
- Example 1 - level 1 heading on calling page
For example:
= Earthing (electrical) = {{:Earthing (electrical)}}
This will also include categories from the original page (unless they are inside a <noinclude> tag where they occur on the original page).
- Example 2 - level 2 heading on transcluded page
The header also can be placed in the page to be transcluded, such as:
{{:Welcome to Appropedia/Selected project/Nominations}}
with its category not transcluded, such as:
<noinclude> [[Category:Welcome to Appropedia|{{SUBPAGENAME}}]] </noinclude>
This produces: Welcome to Appropedia/Selected project/Nominations