The difference between single quotes and double quotes when declaring strings

The difference and connection between the grammatical structures of heredoc and nowdoc

heredoc and nowdoc initialize local variables and class attributes

Detailed explanation of two syntaxes and examples of variable parsing

String addition, deletion, modification and search operations

Substring processing substr and related functions

String retrieval functions strpos() and strstr()

String padding and replacement str_pad() and str_replace()

String length statistics strlen() and mb_strlen(), mb_strwidth()

Splitting and combining strings explode() and implode()

Detailed explanation of character type conversion [temporary/permanent/automatic]

String formatting function [Key points]

String content filtering and transcoding

String serialization and JSON processing [Key points]