Build a small plain-text editor with visible text and Find/Replace fields.
Support literal search, Match case and ASCII whole-word matching.
Use this five-line sample: cat, Cat, catalog, cat_1, cat (one entry per line).
Count must leave the text unchanged.
With whole words on and Match case off, replacing cat with dog changes 3 entries.
Keep catalog and cat_1 unchanged.
A second identical replacement must report 0 and preserve the text.
Provide Undo for the last replacement, preserving the prior text exactly.
Provide Reset and a UTF-8 text download with no added newline.
Changing search options must update the count before a replacement.
Keep text in the current page without automatic saving or submission.
Include run instructions and actual results for these checks.