 As I said, regular expression is nothing but a pattern recognition. So whenever you will plan to use regular expression in any of your application, then the first thing what you need to do is identify the pattern on which you want to do some operation. So let's take an example from our previous module where we replace the title from the given name list with the empty string. Now let's try to understand how it works. So here I have defined one regex and one input source. Now this input source contain the list of names from which I want to find the title. Now before we go ahead, let's try to understand the each elements used in the regex pattern through one online tool to get some idea. Alright, so this is a good online regex testing tool with different flavors of engine. Here I have defined the input source on which I want to perform some operation. Say at least in this case, I want to find all the titles defined in this input source. Okay, so now let's start to build the regex. Okay, now here before we start writing, let us first identify the pattern here in the input source. We have a title mister followed by either a dot or followed by a space. Same way miss either followed by dot or there may be a space. So what I want is I want to find this title by writing the regex. So first let us find the mister. Now here I also want to find the dot, but dot has a special meaning in the world of regex expression as it is a language element. So we need to treat as a literal character and for that we need to use a backslash followed by dot. Now here backslash is also called a character escape and to make the dot optional, I need to use the question mark character. Now this question mark character is called quantifiers. Don't worry, we will understand this each language elements in detail later on in this module and then there is a space. So the first pattern is ready now. Now at the same time I also want to find the other titles such as mister, misses, etc. So for that I need to use here a pipe sign. Now this pipe sign is called an alternation construct. In simple language this is called either or operation means in our case identify pattern which either contain title mister or miss or misses. So now let us find the misses pattern for that followed by dot and space and then alternation followed by miss which may contain dot or may not contain dot. So I make it optional. Okay, so this is how it matches the pattern and highlighting all the matching elements here. Alright, now let's moving to our presentation part. Alright, so now we have regex and input source is ready. Now next you send both this input source you want to test as well as the regular expression to a regex function. In real world scenario this input source will normally be a text string or a group of string or a database tables data or any arbitrary data for which you are using the regular expression. Because the function has received both the input source as well as the regex it will go to the regex engine which will compile the regex and generate the string and returning the result as output. Now depending on the regex function used you will either get a true or a false type of result or a number of count of matches or some array string with matches which you can use further for processing.