History search matching anywhere

I believe the current history search matches from the start of the string. Could it be updated with an option for matching anywhere in the string?

The enable_history_search could perhaps be updated where the current True and False settings do as they have done, but now there are additional options for enable_history_search=:

• 'starts-with' (same as current enable_history_search=True setting)
• 'contains' (matches anywhere in the string).

I may not understand the classes right, but I'm looking at making the change... my thoughts are below:

The actual string search part at each line is hopefully easy, assuming basic python strings are actually used internally:

>>> "King" in "King's landing"
True

>>> "Jon Snow" in "King's landing"
False

Start by locating the implementation and tests for the enable_history_search setting, then read how its current True and False modes choose history matches. Define the behavior for the proposed 'starts-with' and 'contains' options, preserve existing boolean behavior, and verify both matching modes with the relevant history-search tests.