RegEx can be used to find text between tags in Salesforce using Apex.

Sample Code:

String str = '<test>abc</test><test>xyz</test>'; 
Pattern TAG_REGEX = Pattern.compile( 
    '<test>[a-z]*</test>' 
); 
Matcher matcher = TAG_REGEX.matcher( 
    str 
); 
while ( matcher.find() ) { 
    
    String strOutput = matcher.group().replace( 
        '<test>', '' 
    ).replace( 
        '</test>', '' 
    ); 
    System.debug( 
        strOutput 
    ); 
    
}

Output:

Sample Code with Capital Letters and Space:

String str = '<test>abc ABC+</test><test>xyz XYZ-</test>';
Pattern TAG_REGEX = Pattern.compile( 
	'<test>[a-zA-Z0-9\\s+-]*</test>' 
);
Matcher matcher = TAG_REGEX.matcher( 
	str 
);

while ( matcher.find() ) {

    String strOutput = matcher.group().replace( 
		'<test>', '' 
	).replace( 
		'</test>', '' 
	);
    System.debug( 
		strOutput 
	);


}

Output: