Use of Regular Expressions in PHP

Let's look at the regular expression in PHP today, where there is a PCRE mode. I mean, there are different regular expressions? For example, in some cases, the dot code A, but in another case, does the DoT number represent B? So what are the mainstream regular expression patterns? Let's look at the regular expression in PHP today, where there is a PCRE mode. I mean, there are different regular expressions?
For example, in some cases, the dot code A, but in another case, does the DoT number represent B?
So what are the mainstream regular expression patterns?

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Let's look at the regular expression in PHP today, where there is a PCRE mode. I mean, there are different regular expressions?
For example, in some cases, the dot code A, but in another case, does the DoT number represent B?
So what are the mainstream regular expression patterns?

There are two main methods: PCRE and POSIX. The basic idea is the same according to the environment, but some details are different and there are some things I don't know, let's take a look at the corresponding descriptions in the PHP help document.