[Search] add alternate search modes and regex search

[bhajneet]

From regex tutorial:

Because we want to do more than simply search for literal pieces of text, we need to reserve certain characters for special use. In the regex flavors discussed in this tutorial, there are 12 characters with special meanings: the backslash \, the caret ^, the dollar sign $, the period or dot ., the vertical bar or pipe symbol |, the question mark ?, the asterisk or star *, the plus sign +, the opening parenthesis (, the closing parenthesis ), the opening square bracket [, and the opening curly brace {, These special characters are often called "metacharacters". Most of them are errors when used alone.

So to implement regex, one would have to avoid these chars for our alternate search modes: \^$.|?*+()[]{}. Note that \^|[] are used in gurmukhi ASCII (though [] are line endings). Need to see if it can be reconciled. (Perhaps only allow those chars in GUI keyboard? Or perhaps re-route these to a different keyboard character in our app that is non-standard to the font spec?).

Alternate search mode proposals:

• % before or after a word can be like SQL LIKE where it allows any characters before or after that word
• ~ can be words without accents. This is also an ASCII char in gurmukhi...
• ! and / should be bangs or commands. Example bang would be !sggs to filter out only sggs results.
• Typing just numbers should show page numbers of various sources as results. One could use a colon to signify line number (e.g. 123:4 would be the fourth line of the 123rd page of any matching sources).

Regex ideas:

• Can we somehow prepending search input with ^ char? It would be regex begins with (so #^ means the word must be at the beginning of the line or heavy pause, ^jkms means they are first letters from start of line). Note ^ symbol is Khakka pair bindi in ASCII
• Appending search input with $ = Ends with (see above for ideas behind logic).

If you have more ideas, please feel free to discuss.

Related Issues:

• [ ] Add full word strict #147

[bhajneet]

Note, if doing normal first letter anywhere search, hitting the spacebar should be adding a wild card character. That wild card character can be converted to a . char, similar to regex.

If we decide not to do regex, perhaps the _ or * characters would make more sense for wildcard conversion.