regex_search trying to match a string containing '[' - regex

Question

Being relatively new to regular expressions I am having trouble figuring out the correct syntax. I am trying to match a string with the following pattern: String[string]!='string'. I want to divide it into three matches as it follows:
String[string] // can contain numbers
!= // operator that can also be: =,> and < or a combination of these
'string' // can contain _ and numbers
So far I have managed to match a string with the following pattern: string='string'. Using this code:
const string strExpression = "TypeValue!='Set_Site'";
regex regex("([a-zA-Z0-9]+)([=><!]+)(['a-zA-Z0-9_]+)");
smatch match;
if (regex_search(strExpression.begin(), strExpression.end(), match, regex))
{
string indicator(match[1]);
string op(match[2]);
string value(match[3]);
}
However when I try to add '[' and ']' to the regex syntax I don't get any matches. I have modified the code like this:
const string strExpression = "Type[Value]!='Set_Site'";
regex regex("([]a-zA-Z0-9[]+)([=><!]+)(['a-zA-Z0-9_]+)");
smatch match;
if (regex_search(strExpression.begin(), strExpression.end(), match, regex))
{
string indicator(match[1]);
string op(match[2]);
string value(match[3]);
}
Аccording to the documentation I am reading the right-square-bracket ( ']' ) will lose its special meaning (terminating the bracket expression) and represent itself in a bracket expression if it occurs first in the list. For the left-square-bracket( '[' ) it says that it will lose its special meaning within a bracket expression. So following this rules and definitions I cannot identify why i am not getting any matches
Can someone give me some guidelines what I am doing wrong?
Thank you.