Odd Regex Escape

Example Script

#this is all powershell, but its using the .net Escape()
#i've also made it use the .net match() with similar results.
#based on the MSDN docs it looks like it doesnt need to escape a ], which makes sense if there is no open

$chars = "abcd[]."
"a","b" | %{ $_ -match "[$([regex]::Escape($chars))]"}
[regex]::Match("a","[$([regex]::Escape($chars))]").Success

#output is all false

$escchars = "abcd\[\]\."
"a","b" | %{ $_ -match "[$escchars]"}
[regex]::Match("a","[$escchars]").Success

#output is all true

MSDN Doc

http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.escape%28v=vs.110%29.aspx

Regex.Escape Method

"While the Escape method escapes the straight opening bracket ([) and opening brace ({) characters, it does not escape their corresponding closing characters (] and }). In most cases, escaping these is not necessary. If a closing bracket or brace is not preceded by its corresponding opening character, the regular expression engine interprets it literally. If an opening braket or brace is interpreted as a metacharacter, the regular expression engine interprets the first corresponding closing character as a metacharacter. If this is not the desired behavior, the closing bracket or brace should be escaped by explicitly prepending the backslash (\) character. For an illustration, see the Example section."