Using a local development environment with:
xampp-win32-7.2.1-0-VC15-installer
Windows NT SCDLSERVER 10.0 build 16299 (Windows 10) i586
Apache/2.4.29 (Win32) OpenSSL/1.1.0g PHP/7.2.1
My configuration has \\SCDLSERVER\xampp\htdocs\scdl as it's root. I have 3 files: header.html, index.html, and content\links.html
header.html is included (with php include) in index.html with include('header.html') and in content\links.html with include('../header.html').
header.html has an <IMG SRC="graphics/logo.jpg"...>.
When rendered from index.html it works. That is the image is looked for and FOUND in /scdl/graphics/logo.jpg as it should. When rendered from links.html it fails. That is the image is looked for and NOT FOUND in /scdl/content/graphics/logo.jpg.
Furthermore, links.html itself contains HREFs to other files. When rendered from index.html it works (looks for the files in /scdl/content); but does not work from links.html (looks for the files in /scdl/content/content).
PHP testing code indicates the full path is C:\xampp\htdocs\scdl in all cases.
I have googled this several times over the last 3-4 days and reviewed the postings here. All I found suggests it should be working as expected.
What am I missing?