NewTemplatedHelpHandler uses custom application, usage, flag, and argument
templates. They consume preformatted labels and defaults and write help to stdout.
The same layout is used for explicit help and input-error responses.
Tabs in the entry templates separate label and description columns. Alignment
and word wrapping are automatic, using the output terminal's width or 80 columns
for redirected output. WithWidth(n) fixes the width; WithFormatting(false)
preserves the rendered template bytes instead.
Run from the repository root:
mise example custom-help --help
# Help for custom-help
# A greeting with a custom help layout.
#
# Run: custom-help [flags] <name>
#
# Inputs:
# <name>: Name to greet. [required]
#
# Options:
# -g, --greeting=<greeting>: Greeting to use. [default: Hello]
# -h, --help: Show help.
mise example custom-help Carl
# Hello, Carl!
mise example custom-help --unknown
# Error: unknown flag --unknown
# <custom help layout>
# program exit code: 2