WIP

9-regular-expressions/04-regexp-anchors/1-start-end/solution.md

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+An empty string is the only match: it starts and immediately finishes.
+
+The task once again demonstrates that anchors are not characters, but tests.
+
+The string is empty `""`. The engine first matches the `pattern:^` (input start), yes it's there, and then immediately the end `pattern:$`, it's here too. So there's a match.

9-regular-expressions/04-regexp-anchors/1-start-end/task.md

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+# Regexp ^$
+
+Which string matches the pattern `pattern:^$`?

9-regular-expressions/04-regexp-anchors/article.md

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+# Anchors: string start ^ and end $
+
+The caret `pattern:^` and dollar `pattern:$` characters have special meaning in a regexp. They are called "anchors".
+
+The caret `pattern:^` matches at the beginning of the text, and the dollar `pattern:$` -- at the end.
+
+For instance, let's test if the text starts with `Mary`:
+
+```js run
+let str1 = "Mary had a little lamb";
+alert( /^Mary/.test(str1) ); // true
+```
+
+The pattern `pattern:^Mary` means: "string start and then Mary".
+
+Similar to this, we can test if the string ends with `snow` using `pattern:snow$`:
+
+```js run
+let str1 = "it's fleece was white as snow";
+alert( /snow$/.test(str1) ); // true
+```
+
+In these particular cases we could use string methods `startsWith/endsWith` instead. Regular expressions should be used for more complex tests.
+
+## Testing for a full match
+
+Both anchors together `pattern:^...$` are often used to test whether or not a string fully matches the pattern. For instance, to check if the user input is in the right format.
+
+Let's check whether or not a string is a time in `12:34` format. That is: two digits, then a colon, and then another two digits.
+
+In regular expressions language that's `pattern:\d\d:\d\d`:
+
+```js run
+let goodInput = "12:34";
+let badInput = "12:345";
+
+let regexp = /^\d\d:\d\d$/;
+alert( regexp.test(goodInput) ); // true
+alert( regexp.test(badInput) ); // false
+```
+
+Here the match for `pattern:\d\d:\d\d` must start exactly after the beginning of the text `pattern:^`, and the end `pattern:$` must immediately follow.
+
+The whole string must be exactly in this format. If there's any deviation or an extra character, the result is `false`.
+
+Anchors behave differently if flag `pattern:m` is present. We'll see that in the next article.
+
+```smart header="Anchors have \"zero width\""
+Anchors `pattern:^` and `pattern:$` are tests. They have zero width.
+
+In other words, they do not match a character, but rather force the regexp engine to check the condition (text start/end).
+```