Why isn't this Vim syntax command in after/ftplugin/yaml.vim working? -

Why isn't this Vim syntax command in after/ftplugin/yaml.vim working? -

i have next line in after/ftplugin/yaml.vim

syn match yamlblockmappingkey /^\s*\zs.*\ze\s*:\%(\s\|$\)/

i have tried this:

execute 'syn match yamlblockmappingkey /^\s*\zs.*\ze\s*:\%(\s\|$\)/'

the purpose of create vim highlight keys contain spaces, per this stackoverflow question. problem command doesn't seem work when open new yaml file. know after/ftplugin/yaml.vim beingness sourced, set echom command in there , shows in messages. also, if take line , paste command prompt , execute it, works. know what's up?

the ftplugin scripts sourced before syntax scripts, default yaml syntax clears additional definition. place extension after/syntax/yaml.vim instead; after all, you're extending syntax, not filetype settings.

vim