assistant: Here is the table properly converted to Markdown.
|Regex String|Description|Use Case|Explanation|
|:----|:----|:----|:----|
|^abc|Matches any string that starts with "abc"|To find lines in a text file that start with "abc"|^ asserts the start of a line, and abc is the literal string|
|abc$|Matches any string that ends with "abc"|To find lines in a text file that end with "abc"|abc is the literal string, and $ asserts the end of a line|
|a.b|Matches any string containing "a", any character, and then "b"|To find occurrences of "a" followed by any character and then "b"|a and b are literal characters, and . matches any character except a newline|
|\d{2,4}|Matches a sequence of 2 to 4 digits|To validate a year input with 2 to 4 digits|\d matches any digit, and {2,4} specifies a range of 2 to 4 occurrences|
|[A-Za-z]|Matches any single uppercase or lowercase letter|To find single letters in a text file|[A-Za-z] defines a character class containing all uppercase and lowercase letters|
|[^0-9]|Matches any character that is not a digit|To find non-digit characters in a text file|[^0-9] defines a character class with a negation (^) and a range for digits (0-9)|
|(abc|def)|Matches either "abc" or "def"|To find occurrences of either "abc" or "def" in a text file|
|a{3}|Matches exactly three consecutive "a" characters|To find occurrences of "aaa" in a text file|a is the literal character, and {3} specifies exactly 3 occurrences|
|\bword\b|Matches the word "word" as a whole word|To search for the whole word "word" in a text file|\b asserts a word boundary, and word is the literal string|
|(?i)abc|Matches "abc" case-insensitively|To find occurrences of "abc" regardless of case|(?i) sets the case-insensitive flag, and abc is the literal string|
|(\d+)\s+|Matches one or more digits followed by one or more whitespace characters|To find and separate numbers followed by spaces in a text file|(\d+) captures one or more digits, and \s+ matches one or more whitespace characters|
|(?<=@)\w+|Matches a word that follows the "@" symbol|To extract usernames from email addresses|(?<=@) is a positive lookbehind for the "@" symbol, and \w+ matches one or more word characters|

assistant: Sure, here are 12 examples of regex strings in a table format:

Regex String	Function	Usage	Breakdown and Explanation
[a-zA-Z]+	Matches any word consisting of only letters, regardless of case.	Used to validate input fields where only letters are allowed, such as names or usernames.	[a-zA-Z] matches any single letter (case-insensitive), and + matches one or more of the preceding expression, resulting in any combination of letters.
\d{3}-\d{2}-\d{4}	Matches a social security number in the format of XXX-XX-XXXX.	Used for validating social security number inputs.	\d matches any digit, and {3}, {2}, and {4} specify the exact number of digits to match in each group. The hyphens are also included as literal characters to match.
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$	Matches a password that contains at least one lowercase letter, one uppercase letter, and one digit, and is at least 8 characters long.	Used for validating password inputs to ensure they meet complexity requirements.	^ matches the start of the string, (?=.*[a-z]) uses a positive lookahead to ensure at least one lowercase letter is included, (?=.*[A-Z]) ensures at least one uppercase letter is included, (?=.*\d) ensures at least one digit is included, [a-zA-Z\d]{8,} matches any combination of letters and digits that is at least 8 characters long, and $ matches the end of the string.
^\d{4}$	Matches a 4-digit PIN.	Used for validating PIN inputs.	^ matches the start of the string, \d matches any digit, {4} specifies that exactly 4 digits must be matched, and $ matches the end of the string.
^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$	Matches an email address.	Used for validating email inputs.	^ matches the start of the string, [\w-\.]+ matches any combination of word characters, hyphens, and periods (to allow for email addresses with subdomains), @ matches the literal '@' symbol, ([\w-]+\.)+ matches one or more instances of a group consisting of word characters and a period (to allow for email addresses with multiple subdomains), [\w-]{2,4} matches the top-level domain (e.g. com, org, net), which can be between 2 and 4 characters long, and $ matches the end of the string.
^http[s]?://[a-z]+\.[a-z]{2,}$	Matches a URL starting with "http://" or "https://" and ending with a domain name.	Used for validating URL inputs.	^ matches the start of the string, http[s]?:// matches either "http://" or "https://", [a-z]+\. matches one or more letters followed by a period (to match the domain name), [a-z]{2,} matches the top-level domain (e.g. com, org, net), which can be between 2 and any number of characters long, and $ matches the end of the string.
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?\d3?[-.\s]?\d{3}[-.\s]?\