[Regexp] What regular expression to use

Hello!

I have the following text:

<textfragment>
[{{a, b, c}, 
{d, e, f}}]

[a+b]

a[i]

sum(a[i],i,n1,n2)

root[i](a0, ..., an)
</textfragment>

From this text, I want to find all text blocks enclosed by brackets ([
and ]).

Sometimes, these brackets have other meaning (like a[i] and root[i]).

Therefore, I want to create a regular expression, which 

1) finds all text blocks enclosed by brackets, provided
2) that the character before the "opening" bracket [ isn't an
alphanumeric character.

In other words, that regular expression should find two text blocks in
the above example, namely

a) [{{a, b, c}, 
{d, e, f}}]

b) [a+b]

I've tried following regular expressions, but neither of them produced
exactly that result:

<code>
//regularExpression=new RE("[\\n\\r\\s]\\[(.*)\\]",
RE.REG_DOT_NEWLINE);
//regularExpression=new RE("[^a-zA-Z]\\\[.*\\]", RE.REG_DOT_NEWLINE);

regularExpression=new RE("\\n\\[(.*)\\]", RE.REG_DOT_NEWLINE);
				
matches=regularExpression.getAllMatches(area.getText());
for (int i=0;i < matches.length ; i++ )
{
	System.out.println("-----");
	System.out.println(matches[i].toString(0));
}
</code>

This piece of code should print following text:

a) {{a, b, c}, 
{d, e, f}}

b) a+b

What am I doing wrong?

TIA

dap