Added code examples to introduction doc.

exercises/concept/little-sisters-essay/.docs/introduction.md

@@ -1,9 +1,108 @@
 # Introduction
 
-Python provides several useful methods that can be used to manipulate strings.
-These methods can be used for cleaning, splitting, translating, or otherwise working with any object of type `str`.
-Strings can be concatenated using the `+` operator or with the `str.join()` method.
-Strings also implement all common sequence operations and can be iterated through using the `for item in <string>` syntax.
+The `str` class offers [many useful methods][str methods] for working with and composing strings.
+These include searching, cleaning, splitting, transforming, translating, and many other techniques.
+
+Strings are [immutable sequences][text sequence] of [Unicode code points][unicode code points] (_for more details, see [HOWTO Unicode][howto unicode] in the Python Docs._) -- individual "characters" or code points (_strings of length 1_) can be referenced by `0-based index` number from the left, or `-1-based index` number from the right.
+
+Strings can be iterated through using `for item in <string>` or `for item in enumerate(<string>)` syntax.
+They can be concatenated using the `+` operator or with the `<string>.join()` method, and also implement all [common sequence operations][common sequence operations].
 
 Strings are immutable, meaning the value of a `str` object in memory cannot change.
-That means any functions or methods that operate on a `str` (like the ones we are learning about here) will return a _new instance_ of that `str` instead of modifying the original `str` object.
+Functions or methods that operate on a `str` (_like the ones we are learning about here_) will return a _new instance_ of that `str` instead of modifying the original `str` object.
+
+
+[`<str>.title()`][str-title] parses a string and capitalizes the first "character" of each "word" found.  In Python, this is very dependant on the [language codec][codecs] used, and how the particular language represents words and characters.  There may also be [locale][locale] rules in place.
+
+```python
+man_in_hat_th = 'ู้ชายในหมวก'
+man_in_hat_ru = 'mужчина в шляпе'
+man_in_hat_ko = '모자를 쓴 남자'
+main_in_hat_en = 'the man in the hat.'
+
+>>> man_in_hat_th.title()
+'ผู้ชายในหมวก'
+
+>>> man_in_hat_ru.title()
+'Мужчина В Шляпе'
+
+>>> man_in_hat_ko.title()
+'모자를 쓴 남자'
+
+>> main_in_hat_en.title()
+'The Man In The Hat.'
+```
+
+[`<str>`.endswith(<suffix>)][str-endswith] returns `True` if the string ends with `<suffix>`, `False` otherwise.
+
+```python
+>>> 'My heart breaks. 💔'.endswith('💔')
+True
+
+>>> 'cheerfulness'.endswith('ness')
+True
+
+>>> 'Do you want to 💃?'.endswith('💃')
+False
+
+>> 'The quick brown fox jumped over the lazy dog.'.endswith('dog')
+False
+```
+
+[`<str>`.strip(<chars>)][str-strip] returns a copy of the `str` with leading and trailing `<chars>` removed.
+The code points specified in `<chars>` are not a prefix or suffix - all combinations of the code points will be removed starting from both ends of the string.
+ If nothing is specified for `<chars>`, all combinations of whitespace will be removed.
+
+ ```python
+ >>> 'https://unicode.org/emoji/'.strip('/stph:')
+'unicode.org/emoji'
+
+>>> '   🐪🐪🐪🌟🐪🐪🐪   '.strip()
+'🐪🐪🐪🌟🐪🐪🐪'
+
+>>> justification = 'оправдание'
+>>> justification.strip('еина')
+'оправд'
+
+>>> 'unaddressed'.strip('dnue')
+'address'
+
+>>> '  unaddressed  '.strip('dnue ')
+'address'
+```
+
+[`<str>.replace(<substring>, <replacement substring>)`][str-replace] returns a copy of the string with all occurences of `<substring>` replaced with `<replacement substring>`.
+
+```python
+# Quote from The Hunting of the Snark, by Lewis Carroll
+>>> quote = '''
+"Just the place for a Snark!" the Bellman cried,
+   As he landed his crew with care;
+Supporting each man on the top of the tide
+   By a finger entwined in his hair.
+
+"Just the place for a Snark! I have said it twice:
+   That alone should encourage the crew.
+Just the place for a Snark! I have said it thrice:
+   What I tell you three times is true."
+'''
+
+>>> quote.replace('Snark', '🐲')
+...
+'\n"Just the place for a 🐲!" the Bellman cried,\n   As he landed his crew with care;\nSupporting each man on the top of the tide\n   By a finger entwined in his hair.\n\n"Just the place for a 🐲! I have said it twice:\n   That alone should encourage the crew.\nJust the place for a 🐲! I have said it thrice:\n   What I tell you three times is true."\n'
+
+>>> 'bookkeeper'.replace('kk', 'k k')
+'book keeper'
+```
+
+[str methods]: https://docs.python.org/3/library/stdtypes.html#string-methods
+[text sequence]: https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str
+[unicode code points]: https://stackoverflow.com/questions/27331819/whats-the-difference-between-a-character-a-code-point-a-glyph-and-a-grapheme
+[common sequence operations]: https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str
+[str-title]: https://docs.python.org/3/library/stdtypes.html#str.title
+[str-endswith]: https://docs.python.org/3/library/stdtypes.html#str.endswith
+[str-strip]: https://docs.python.org/3/library/stdtypes.html#str.strip
+[str-replace]: https://docs.python.org/3/library/stdtypes.html#str.replace
+[codecs]: https://docs.python.org/3/library/codecs.html
+[locale]: https://docs.python.org/3/library/locale.html#module-locale
+[howto unicode]: https://docs.python.org/3/howto/unicode.html