Steps to reproduce

$herestr=@"
'"'
"@
Write-Host $herestr

Expected behavior

A string containing a single-quote, a double quote and another single quote should be printed to stdout.
According to Powershell "about quoting rules":
A here-string is a single-quoted or double-quoted string in which quotation marks are interpreted literally.

Actual behavior

A TerminatorExpectedAtEndOfString is thrown in version 5.0 (with version 2.0 the actual behaviour is as expected).
If I escape the last single quote with a backtick the behaviour is also as expected in V5.0

Environment data

Powershell version 5.0 (build 10586, revision 117) throws the exception.
In a Powershell version 2.0 it works as expected

Additional information

According to feedback I received on superuser.com escaping the single quote is not the only way to work around this. Other options are:

You can workaround this by putting extra space: $herestr =@"... or $herestr= @"...; or by enclosing in parenthesis: ($herestr=@"..."@)
The option of enclosing in parenthesis causes the here document to be echoed but I can confirm that these options work in V5.0 (build 10586, revision 117)