Rationale for Undefined Keys in Search Mode #263

Is your feature request related to a problem? Please describe.
Not a problem per se. Every fuzzy search plugin in Vim is different, but certain features are shared by multiple plugins. In particular, many fuzzy searchers can include punctuation characters in a search query, either as literal characters or special characters for regex-based queries. I was surprised that this plugin generates an error message " Key doesn't work in this view." I managed to make some test queries search for literal period characters with

let g:CtrlSpaceKeys = {'Search': {'.': 'ctrlspace#keys#search#AddLetter'}}

Is there any reason I shouldn't do this? There must be a reason this isn't enabled by default, right?

Describe the solution you'd like
An explanation of the default keymappings and the consequences of modifying them.

Version(s) (please complete the following information):

• OS:
  Ubuntu 18.04 (technically the ubuntu:18.04 docker image)
• :version
  NVIM v0.4.3
  Build type: RelWithDebInfo
  LuaJIT 2.0.5
  Compilation: /usr/bin/gcc-5 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -O2 -g -DMIN_LOG_LEVEL=3 -Og -g -Wall -Wextra -pedan
  tic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wshadow -Wconversion -Wmissing-prototypes -Wvla -fstack-prot
  ector-strong -fdiagnostics-color=auto -DINCLUDE_GENERATED_DECLARATIONS -D_GNU_SOURCE -DNVIM_MSGPACK_HAS_FLOAT32 -DNVIM
  _UNIBI_HAS_VAR_FROM -I/home/travis/build/neovim/bot-ci/build/neovim/build/config -I/home/travis/build/neovim/bot-ci/bu
  ild/neovim/src -I/home/travis/build/neovim/bot-ci/build/neovim/.deps/usr/include -I/usr/include -I/home/travis/build/n
  eovim/bot-ci/build/neovim/build/src/nvim/auto -I/home/travis/build/neovim/bot-ci/build/neovim/build/include
  Compiled by travis@travis-job-9a287301-34f2-4b86-92e3-462594f51f36

Features: +acl +iconv +tui

system vimrc file: "$VIM/sysinit.vim"
fall-back for $VIM: "/home/travis/build/neovim/bot-ci/build/neovim/build/nvim.AppDir/usr/share/nvim"