#include<bits/stdc++.h>
using namespace std;
//#define int long long
#define rep(i,j,k) for(int i=(j);i<=(k);i++)
#define per(i,j,k) for(int i=(j);i>=(k);i--)
#define pb emplace_back
#define fi first
#define se second
using vi=vector<int>;
using pi=pair<int,int>;

void solve(){
	int n,m; cin>>n>>m;
	vector<vi> a(n, vi(m));
	vi s(n+m), c(n+m);
	rep(i,0,n-1){
		string str; cin>>str;
		rep(j,0,m-1){
			a[i][j]=(str[j]=='B');
		}
	}
	rep(i,0,n-1){
		rep(j,0,m-1){
			s[i+j]^= a[i][j];
			c[i+j]^= 1;
		}
	}

	vector<vi> ans;
	auto opt=[&](vi d){
		ans.pb(d);
		
		int c=0;
		rep(i,0,n-1){
			a[i][c]^= 1;
			while(c<d[i+1]){
				c++;
				a[i][c]^= 1;
			}
		}
	};

	auto slv=[&](int op){
		ans.clear();
		rep(i,1,n+m-2){
			if(op==0 && s[i]!=s[i-1]){
				return false;
			}
		}
		rep(i,0,n+m-2){
			if(op==1 && s[i]!=c[i]){
				return false;
			}
		}
		per(i,n-1,-(m-2)){// i=x-y
			vi d(n+1, m-1);
			d[0]=0;
			rep(x,1,n-1){
				int y=x-i;
				if(y<0){
					d[x]=0;
				}
				else if(y>=m-1){
					d[x]=m-1;
				}
				else{
					if(a[x][y]!=op){
						d[x]=y;
					}
					else{
						d[x]=y+1;
					}
				}
			}
			opt(d);
		}
		if(a[0][m-1]!=op){
			vi d(n+1, m-1);
			d[0]=0;
			opt(d);
		}
		return true;
	};
	
	bool ok=0;
	rep(c,0,1){
		if(slv(c)){
			ok=1;
			break;
		}
	}

	if(!ok){
		cout<< "NO\n";
		return;
	}
	cout<< "YES\n";
	cout<< ans.size() <<'\n';
	for(auto x:ans){
		//for(int y:x){
		//	cout<< y <<' ';
		//}
		//cout<<endl;
		string output;
		int c=0;
		rep(i,1,n){
			while(c<x[i]){
				output+= 'R';
				c++;
			}
			if(i<n){
				output+= 'D';
			}
		}
		cout<< output <<'\n';
	}
}
signed main(){
	ios::sync_with_stdio(0);cin.tie(0);
	#ifndef ONLINE_JUDGE
	assert(freopen(".in","r",stdin));
	assert(freopen(".out","w",stdout));
	#endif
	
	int t; cin>>t;
	while(t--){
		solve();
	}
}