anchor.diff:  
   ENV PHP_VERSION           ${VERSION}
   ENV PHP_VERSION_MAJOR     7
  -ENV PECL_XDEBUG_VERSION   2.5.0
   ENV PECL_YAML_VERSION     2.0.0
   
   RUN set -x \
  
positive.code:     ## composer
      && wget -q -O - https://getcomposer.org/installer \
           | php --  --install-dir=/usr/local/bin --filename=composer \
      ## xdebug
      && apk --no-cache add --virtual .builddeps \
          autoconf \
          automake \
          bash \
          build-base \  
          file \
          git \
          re2c \
  
negative.code:     && apk --no-cache add --virtual .builddeps.edge \
          --repository http://dl-cdn.alpinelinux.org/alpine/edge/community/ \
          php${PHP_VERSION_MAJOR}-dev \
      ## yaml
      && wget -q -O - https://pecl.php.net/get/yaml-${PECL_YAML_VERSION}.tgz \
          | tar -xzf - -C /tmp \
  