Checking on validation errors...

Installed Validate Document Extension in the browser - Alt+Shift+V,
on some websites you see 46 validation errors.
Like from a random example as listed up from inside the browser console (Ctrl+Shift+I)

VM61:1 line 13: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 17: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 34: Bad value “//fonts.googleapis.com/css?family=Playfair+Display:400,400i,700,700i|Domine:400,700” for attribute “href” on element “link”: Illegal character in query: “|” is not allowed. eval @ VM61:1 VM61:1 line 35: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 36: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 47: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 48: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 48: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 49: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 50: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 50: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 50: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 51: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 51: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 52: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 52: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 53: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 53: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 54: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 54: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 55: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 55: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 55: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 56: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 56: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 56: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 57: CSS: “font-family”: Parse Error. eval @ VM61:1 VM61:1 line 57: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 57: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 57: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 57: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 58: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 58: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 59: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 59: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 59: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 60: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 60: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 60: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 61: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 61: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 62: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 62: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 62: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 63: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 63: CSS: “font-weight”: Parse Error. eval @ VM61:1 VM61:1 line 63: CSS: “font-style”: Parse Error. eval @ VM61:1 VM61:1 line 63: CSS: “line-height”: Parse Error. eval @ VM61:1 VM61:1 line 65: CSS: “font-size”: Parse Error. eval @ VM61:1 VM61:1 line 70: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 78: CSS: Parse Error. eval @ VM61:1 VM61:1 line 128: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 129: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 132: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 139: The “type” attribute for the “style” element is not needed and should be omitted. eval @ VM61:1 VM61:1 line 175: The “navigation” role is unnecessary for element “nav”. eval @ VM61:1 VM61:1 line 580: The “navigation” role is unnecessary for element “nav”. eval @ VM61:1 VM61:1 line 733: Duplicate ID “theiaStickySidebar”. eval @ VM61:1 VM61:1 line 589: The first occurrence of ID “theiaStickySidebar” was here. eval @ VM61:1 VM61:1 line 826: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 827: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 828: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 829: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM61:1 line 830: The “type” attribute is unnecessary for JavaScript resources. eval @ VM61:1 VM62:1 46 validation errors VM62:1 46 validation errors

This could help web developers greatly with a quick and dirty, but also could pinpoint out page-errors in general.
Could be issues like this

You have this (random example):

<img src=“numbers-01.jpg” alt=">

Should be this:

(info source treehouse community - Jason Anello)

polonus (volunteer 3rd party cold recon website security analyst and website error-hunter)

There is also an online validation check from the real makers of these standards:
https://validator.w3.org/check?uri=
After all w3 dot org is the organization that sets such standards. (info: Ron625).

polonus