how do I chain regular expressions together?
You can chain regular expressions together by using the `|` (pipe) symbol. The pipe symbol is used to indicate a "or" relationship between the two expressions. For example, the following regular expression: `a|b` will match either the character `a` or the character `b`.
 To chain regular expressions together, you can apply one regular expression to the output of another regular expression. This can be done using programming languages that support regular expressions, such as Python, JavaScript, and Java. Here's an example using Python:
```python
import re

text = "The quick brown fox jumps over the lazy dog."

# First regular expression to extract words starting with 'f'
regex1 = r'\bf\w*\b'
result1 = re.findall(regex1, text)
print(result1)  # ['fox']

# Second regular expression to extract words with 3 or more letters
regex2 = r'\b\w{3,}\b'
result2 = re.findall(regex2, ' '.join(result1))
print(result2)  # ['fox']
```
In this example, we first extract words starting with 'f' using `regex1` and then apply `regex2` to extract words with 3 or more letters from the output of `regex1`.

Alternatively, you can also use a single regular expression with multiple patterns separated by the `|` symbol to match multiple conditions. Here's an example:
```python
import re

text = "The quick brown fox jumps over the lazy dog."

regex = r'\bf\w*\b