Explanation of Code on Page 78 (UITextFieldDelegate)

Hi,
The syntax for UITextFieldDelegate is gives as
“f​u​n​c​ ​t​e​x​t​F​i​e​l​d​(​t​e​x​t​F​i​e​l​d​:​ ​U​I​T​e​x​t​F​i​e​l​d​,​
​ ​ ​ ​ ​ ​ ​ ​s​h​o​u​l​d​C​h​a​n​g​e​C​h​a​r​a​c​t​e​r​s​I​n​R​a​n​g​e​ ​r​a​n​g​e​:​ ​N​S​R​a​n​g​e​,​
​ ​ ​ ​ ​ ​ ​ ​r​e​p​l​a​c​e​m​e​n​t​S​t​r​i​n​g​ ​s​t​r​i​n​g​:​ ​S​t​r​i​n​g​)​ ​-​>​ ​B​o​o​l​ ​{​

​ ​ ​ ​p​r​i​n​t​(​"​C​u​r​r​e​n​t​ ​t​e​x​t​:​ ​\​(​t​e​x​t​F​i​e​l​d​.​t​e​x​t​)​"​)​
​ ​ ​ ​p​r​i​n​t​(​"​R​e​p​l​a​c​e​m​e​n​t​ ​t​e​x​t​:​ ​\​(​s​t​r​i​n​g​)​"​)​

​ ​ ​ ​r​e​t​u​r​n​ ​t​r​u​e​

​ ​ ​ ​l​e​t​ ​e​x​i​s​t​i​n​g​T​e​x​t​H​a​s​D​e​c​i​m​a​l​S​e[…]”

Excerpt From: Keur, Christian. “iOS Programming: The Big Nerd Ranch Guide (Nikhil Pandey’s Library).” Big Nerd Ranch Guides, 2015-12. iBooks.
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Can anyone please explain what is basic syntax , which is given below
“f​u​n​c​ ​t​e​x​t​F​i​e​l​d​(​t​e​x​t​F​i​e​l​d​:​ ​U​I​T​e​x​t​F​i​e​l​d​,​
​ ​ ​ ​ ​ ​ ​ ​s​h​o​u​l​d​C​h​a​n​g​e​C​h​a​r​a​c​t​e​r​s​I​n​R​a​n​g​e​ ​r​a​n​g​e​:​ ​N​S​R​a​n​g​e​,​
​ ​ ​ ​ ​ ​ ​ ​r​e​p​l​a​c​e​m​e​n​t​S​t​r​i​n​g​ ​s​t​r​i​n​g​:​ ​S​t​r​i​n​g​)​ ​-​>​ ​B​o​o​l​ ​{​
}
What is shouldChangeCharactersInRage and then it’s range: NSRange, also replacementString string: String. Are shouldChangeCharactersInRange and replacementString are functions inside the textFieldDelegate and which take “range” and “string” as parameters, which are of type NSRange and String respectively.