Searching with Wildcards

In the previous examples, regular expressions are constructed with literal characters that match themselves. There are other characters in regex syntax that match in a more generalized way. These are called "metacharacters". Metacharacters do not match themselves, but rather perform a specific task when used in a regular expression. One such metacharacter is the dot ".", or wildcard. When used in a regular expression, the wildcard can match any single character.

Using the wildcard to match any character.

Example 1: Search for the string "ubject".

Regex:
```
.ubject:
```
Matches:
```
Subject:
subject:
Fubject:
```
Doesn't Match:
```
Subject
subject
```

Example 2: Use three dots "..." to search for any three characters within a string.

Regex:
```
t...s
```
Matches:
```
trees
tEENs
t345s
t-4-s
```
Doesn't Match:
```
Trees
twentys
t1234s
```

Example 3: Use several wildcards to match characters throughout a string.

Regex:
```
.a.a.a
```
Matches:
```
Canada
alabama
banana
3a4a5a
```
Doesn't Match:
```
aaa
```