正则表达式：发生后查找下一项

I'm a Go beginner and I've been playing with regexes. Example:

r, _ := regexp.Compile(`\* \* \*`)
r2 := r.ReplaceAll(b, []byte("<hr>"))

(Replace all * * *s for <hr>s)

One thing that I have no idea how to do is to find the next item after an occurence. In JavaScript/jQuery I used to do this:

$("#input-content p:has(br)").next('p').doStuff()

(Find the next p tag after a p tag that has a br tag inside).

What's the simplest way to accomplish the same in Go? Say, finding the next line after * * * ?

* * *

Match this line

You would need to use a capturing group to grap the contents of that sentence:

package main

import "fmt"
import "regexp"

func main() {

    str := `
* * *

Match this line
`   
    r, _ := regexp.Compile(`\* \* \*
.*
(.*)`)

    fmt.Println(r.FindStringSubmatch(str)[1])
}

Output:

Match this line

Explanation:

\* \* \*    Matches the first line containing the asterisks.

          A newline.
.*          Second line. Can be anything (Likely the line is simply empty)

          A newline
(           Start of capturing group
.*          The content of interest
)           End of capturing group

In comments you asked how to replace the third line by <hr/>. In this case I would use two capturing groups - one for the part before the line of interest and one for the line itself. In the replacement pattern you can then use $1 to use the value of the first capturing group in the result.

Example:

package main

import "fmt"
import "regexp"

func main() {

    str := `
* * * 

Match this line
`   
    r, _ := regexp.Compile(`(\* \* \*
.*
)(.*)`)

    str = string(r.ReplaceAll([]byte(str), []byte("$1<hr/>")))

    fmt.Println(str)
}